RESEARCH REPORT / 2026-11-08

Show Just This (cover everything in a screenshot except the part you want to show, all at once) — Research Report

This is an AI translation of the Japanese report. Quotes from Japanese sources are translated, too.

We formed hypotheses from an original idea planned by ChatGPT and Codex (Nov 7) and from the planning agent's plan, "tap the bubble you want to show once, and everything else turns into plain gray shapes," and tested them against official documentation, news reports, research and public records. This is the groundwork for prototype 2026-11-07-h.

In short: Of the 5 hypotheses we formed, 2 were Validated, 2 Partly validated and 1 Validated with conditions. The tools that exist today, whether a chat app's own feature or the automatic hiding features on PCs and phones, all take the form "find what to hide and paint over it." We found no tool whose main idea is "pick only what to show, and cover everything else." The biggest difference is likely to come from filling everything not picked with a solid, non-see-through color, making "one flat image that can't be undone." In 2023, a problem was found in the standard tools on phones and PCs that let the original image be recovered from a cropped image, and there are also cases where mosaic can be undone. Things to watch: if bubble shapes are kept at their original length, they leave a hint about how many characters were written, and we found no survey that measured how many people have had trouble with things slipping into screenshots.

1.Hypothesis validation

5Hypotheses

2Validated

3Partly / with conditions

0Invalidated

Hypothesis	Result	Evidence
Showing or sending screenshots to people is common, and names, notifications and other conversations slipping into them is a real problem	Partly validated	Research: Phone screenshots have been studied as something people "take, keep and share with others." 52 participants submitted their own screenshots and the reasons they took them, and the uses were grouped into 9 themes (a study from a Danish university, presented at an international conference in July 2023) The people who make the apps: The official guide of a chat app (LINE, the messaging app most people in Japan use) suggests turning "conversations that are funny and that you want to share with friends" into images, and says "it's also handy because you can hide the information of the person you're talking with" (updated 2024-08-28). The people who make the app also treat things slipping in as a problem Number of tools: Features that cover emails, phone numbers, faces and so on in screenshots are found in the standard tool on PCs (2023-09), in a paid screenshot tool and in many phone apps What's missing: We found no survey, in Japan or abroad, that measured the share of people who "had trouble because something they didn't want to show slipped into a screenshot" (section 8)
Today's tools take the form "find each thing to hide and paint over it," which leaves effort and missed spots	Validated	The chat app's "Hide information": The official guide only says "icon images and display names switch to dummies." It does not say it hides the text of other people's messages inside the selected range. The range is picked as one continuous band from top to bottom (screens in the guide) The PC's built-in snipping tool: It automatically hides only "emails and phone numbers." Other text is hidden one item at a time by selecting it and right-clicking (official blog, 2023-09-14) The automatic redaction feature of a paid screenshot tool: It finds 9 kinds of data: addresses, card numbers, dates, emails, faces, IP addresses, phone numbers, Social Security numbers and URLs. People's names are not among them (official page) Phone apps: The promo images of an app that blurs chat screenshots also show senders in an email list being covered with a bar one line at a time All of them "hide what they find," so anything not found (a name inside the conversation, a line in a notification and so on) stays as it is (inference)
Painting and blurring can sometimes be undone, so there is a point to making "one flat image that can't be undone"	Validated	Phones' standard editing: It was reported that images cropped or painted with the image markup feature on Google's phones (Pixel) kept the original image at the end of the file, and about 80% could be recovered (CVE-2023-21036, known as aCropalypse; article of 2023-03-20). The article says "the risk of information leaking from screenshots edited before the update remains" The PC's built-in snipping tool: When a saved image was cropped and saved over the same file, the cropped-out part remained (reported 2023-03-28; according to Microsoft, copying and pasting was not affected) Mosaic: A tool was released that recovers text from mosaic if the font and size are known. The researcher wrote "use black bars covering the whole text" (2022-02-15) A government case: Hyogo Prefecture announced that a chart pasted into a Word file was linked to personal data, and editing it exposed the names, addresses, phone numbers and ages of 600 people (2025-12-12). Its measure against a repeat was "make sure to convert to PDF rather than Word format" An article's claim: An article explaining the iPhone's markup feature (Markup) says "depending on the marker, text underneath may show through with brightness adjustments and the like," and recommends using shapes to paint over things reliably (2023-09-03)
A flat PNG that does not contain the original image can be made in the browser alone	Validated with conditions	Official spec: A browser canvas (the part that draws pictures on screen) can turn what was drawn into an image file. If no format is given, it becomes a PNG (MDN) Only the pixels drawn on the canvas are exported, so metadata from the original file (such as when it was taken) and stacked layers are not included (inference; MDN does not say this) Condition: The covering color must be fully opaque. If it is laid on semi-transparently, the brightness of the original text remains in the pixels (inference; the same reason blur and mosaic can be undone)
(Plan) The reverse idea, picking only what to show with 1 tap and covering everything else, makes missed spots unlikely and gets across in 3 seconds	Partly validated	A way of thinking from security: Software security guides call listing dangerous things and blocking them a "massively flawed approach," and say deciding what to let through is more reliable because it "rejects values the developer didn't think of" (OWASP, MDN). Applied to covering, anything not picked is covered from the start, so nothing gets overlooked (applying it this way is our inference) A familiar way of showing: The look of "the picked part stays bright and the rest sinks" is already used in the chat app's range selection screen and in a screenshot tool's spotlight ("dimming and/or blurring the rest of the image"). But in both, the rest can still be read through (they are for showing a range or making something stand out) Something to watch: There is research showing that the "width" of a hidden spot leaks hints about the text inside (about black-box redaction in PDFs, 2023). If bubble shapes are kept at their original length, people can tell who spoke and roughly how many characters they wrote (inference) Whether many people will actually enjoy it can't be known until it is published and we look at the numbers

2.Timing of the story (when, and how far)

2018 The image markup feature on Google's phones arrives with Android 9 (the feature where a problem was later found)
2022-02-15 A security company's researcher releases a tool that recovers text from mosaic, and recommends "cover the text completely with black boxes"
2023-03 The problem of recovering the original from images cropped with the Pixel's markup feature is reported (in Japan on 3/20). On 3/28, the same problem in the PC's built-in snipping tool and its update are also reported
2023-07 The study "why do people take screenshots on their smartphones" is presented at an international conference
2023-09-14 The PC's built-in snipping tool gets a feature that automatically hides emails and phone numbers (starting with the preview version)
2024-08-28 The chat app's official guide "Using the Talk Screenshot feature" (pick a range and turn it into an image; switch icons and display names to dummies) is updated
2025-12-12 Hyogo Prefecture announces that personal information of 600 people was visible from the data of a chart pasted into a Word file
2026-11 Phone app stores list many apps that automatically blur faces and text (as far as we saw in search; when each was released is unverified)

Timing verdict: This is not a topic that heats up with fresh news; it is an everyday problem for anyone with a phone. It drew the most attention with the March 2023 reports that "the original can be recovered from a cropped image." Right now, apps that automatically find and cover things are increasing (inference). If we put it out there, the reverse idea "pick what to show rather than hunting for what to hide" combined with the tip "blur and mosaic can sometimes be undone" seems likely to land well (inference).

3.What the problem really looks like

Who, and whenPeople who take a screenshot on their phone and send it to family, friends or coworkers. Moments like saying "look at this" while showing part of a conversation, a booking or payment screen, or a settings screen. The chat app's official guide also suggests turning conversations into images to share with friends.

What slips inA notification banner that dropped in from the top of the screen (a short message from someone else), the names and icons of other people in the group, and other topics before and after the message you want to show (examples we listed as an inference). The chat app's "Hide information" changes only icons and display names.

Why it happensToday's tools take the form "find what to hide and paint over it." The finding is done either by a person's eyes or by an automatic feature that looks only for set kinds of data (emails, phone numbers and so on), so anything overlooked remains. Depending on how it's painted, a pale color may show through, or the original may be recovered from blur or from data inside the file.

4.Tools and technology today

Tool or technology	What it can do	What it can't do, or what to watch	How we checked
The browser canvas (`toBlob`, which exports an image)	Turns what was drawn into a PNG image. It can be made entirely on the device, without sending the image anywhere	Not officially stated that metadata from the original file is left out (inference). The covering color must be opaque	Official (MDN)
The chat app's "Talk Screenshot"	Long-press a message, pick a range and turn it into an image. "Hide information" switches icons and display names to dummies	Only for conversations inside that app. It is not stated that the text of messages or notifications inside the range is hidden	Official guide (updated 2024-08-28)
The PC's built-in snipping tool (version 11.2308.33.0 and later)	Reads the text in an image and automatically hides emails and phone numbers. Hides selected text	Automatic hiding covers only 2 kinds, emails and phone numbers. Text is read on the device (as explained on the support page)	Official blog (2023-09-14)
Technology that reads text in images (OCR)	When making it real, could be used to find where bubbles and lines are and split them into "units you can pick" (inference)	It misses some text. If used to hide what it finds, it has the same weakness as today's tools (inference)	Inference

5.Competitors, and the gaps

Tool	Who it's for	Price	What it can do	What's missing
LINE's "Talk Screenshot"	People who use LINE	Free (a feature of the app)	Pick a range and turn it into an image, switch icons and display names to dummies, draw on it	Only inside LINE. Other people's messages and notifications inside the range stay as they are (not mentioned in the guide)
Windows Snipping Tool (Quick Redact)	Windows 11 users	Built in	Automatically hides emails and phone numbers, hides selected text	For PCs. Names and conversations are picked one at a time
Snagit Smart Redact	People who make documents from screenshots	Paid (price unverified)	Automatically covers 9 kinds of data, such as addresses, card numbers, emails and faces. The cover can be a box, blur or mosaic, and the official page calls an opaque box the safest	Names are not one of the kinds. For PCs
Snagit Spotlight	People who make manuals	Same as above	Keeps only the picked part bright and darkens or blurs the rest	For making things stand out; the rest can still be read through
Phone apps that blur automatically (e.g. Blur ID)	People who send chat screenshots	Free (with in-app purchases)	Automatically blurs faces, icons and text (according to the app's description)	Hides what it finds. Blur can sometimes be undone. How accurately it finds things is unverified
Phones' standard markup feature	Everyone	Built in	Paint with a pen or boxes	The effort of painting things one by one. A marker can show through (claim of an iPhone article). In 2023 there was also a problem where the cropped original could be recovered (Pixel)

The gaps (where the prototype aims)

A tool whose main idea is "pick what to show, and everything else is filled with an unreadable color": We found none in what we researched. Similar looks exist (range selection, spotlight), but in all of them the rest can still be read through
The same action for a screenshot of any screen: The chat app's feature works only inside that app. A form where notifications and other apps' screens take the same single action too
Showing that it is "one flat image that stays covered even when zoomed in": In light of the 2023 problem, people can check with their own eyes that the original is not left in the saved image
Not relying on automatic finding: Everything not picked is covered, so the worry of "missed finds" doesn't exist in the first place

6.Rules and things to watch

Rule or caution	What it says	In the prototype
Check Sending personal information by mistake (Personal Information Protection Commission)	Its Q&A on information that includes My Number (Japan's national ID number) says that when how it is handled at the place it was mistakenly sent to can't be confirmed, it "may constitute a leak (or a possible leak)." This is not a statement about personal information in general. What it counts as when a screenshot showing customers' names is sent for work should be checked with an expert	Only says "cover before sending." No legal judgments are written
Must fix How to cover (researchers, tool makers)	There are cases where mosaic and blur can be undone. Researchers recommend covering everything with black boxes, and a screenshot tool maker calls an opaque box the safest form	The covering color is opaque. No blur, mosaic or semi-transparency
Must fix How it is saved (phones and PCs in 2023, Hyogo Prefecture in 2025)	Even when something looks hidden, the original data can remain inside the file	Save only a flat PNG that contains no original image or stacked layers
Check Hints from shape and width (research on PDF redaction, 2023)	The width of a hidden spot leaks hints about the text inside	If bubble shapes are kept, round their length to a few sizes or similar, so the original number of characters can't be told
Tip Don't make it look automatically found	The PC's standard tool also hides only 2 kinds automatically, and finding features are assumed to miss things	For your own image, it only paints everything outside the box a person drew in one color. Don't write "the AI found everything"

7.What we put in the prototype

What goes in: One tall screenshot of a phone chat screen (all made up). At the very top, a bar with the time and battery; below it, a notification banner that dropped in from the top (a short message from someone else), the other person's name and icon, the names of other people in the group, the bubble you want to show, and other topics before and after it. The colors and shapes of the bubbles differ from any real chat app. As a second way in, a "Use your own screenshot" button.

What comes out: One image where only the one picked bubble keeps its color and text, and everything else, down to names, icons, notifications and the conversation before and after, becomes opaque gray. It borrows the "only the picked part is bright and the rest sinks" composition of the chat app's range selection screen and a screenshot tool's spotlight from our reference collection (not public). But the rest is a color you can't see through (this is the difference from today's tools). It also shows the saved image arriving in the other person's chat, and that the gray stays gray even when zoomed in there.

Features (up to 3): (1) Pick what to show (tap a bubble once in the sample chat; draw a box on your own image) (2) Cover everything not picked at once in 0.5 seconds, and show in 1 line what was covered (like "Covered names 2, icons 3, notification 1, other messages 5") (3) Save as a flat PNG that can't be undone.

What we leave out, and our promises: Don't make it look like an AI found names or phone numbers (for your own image, it only paints outside the box in one color). Don't use blur, mosaic or semi-transparency to cover. Don't put the original image, stacked layers or the original file's metadata into the saved image (export only the pixels drawn on the canvas). Don't communicate with the outside (no sending to a chat app either). Don't copy the look of real chat apps.

Check If bubble shapes are kept at their original length, people can tell who spoke and roughly how many characters they wrote. Round the length of the gray shapes to 2 or 3 sizes, or keep only left or right (whose message it is). The prototyping agent decides how much to keep and writes it under what we don't know yet.

8.What we couldn’t verify

The share of people who have had trouble with something they didn't want to show slipping into a screenshot (no survey found, in Japan or abroad)
What the 9 themes in the screenshot study are (we read up to the abstract, not the full paper)
Whether range selection in the chat app can skip over bubbles to pick ones that are far apart (not mentioned in the guide; the guide's screens show a continuous range)
That the iPhone markup feature's marker shows through (a claim of an explainer article; we found no official explanation from the maker)
Whether a feature that automatically covers screenshots has been added to the standard features of iOS or Android in 2026 (no official announcement found)
How accurately phone apps that blur automatically find things (only the app descriptions), and the price of the paid screenshot tool and when its automatic redaction feature was released
That a PNG exported from a canvas contains no metadata from the original file (not officially stated; inference)
Whether the thinking in the Personal Information Protection Commission's Q&A applies as is to mistakenly sending personal information other than My Number

Sources (checked 2026-11-08)

LINE user guide: "Using the Talk Screenshot feature" (in Japanese) (updated 2024-08-28; how to pick a range and what "Hide information" changes)
IT University of Copenhagen: Mottelson "Why Do People Take Screenshots on Their Smartphones?" (DIS '23) (2023-07; 52 participants; take, keep, share)
GIGAZINE: "Vulnerability in Google Pixel's screenshot editing feature, with a risk of leaking personal information" (in Japanese) (2023-03-20; the original image remains at the end of the file; about 80% recovered)
The Record: Microsoft patches aCropalypse bug (2023-03-28; the same problem in the PC snipping tool, and when it applies)
Bishop Fox: Never Use Text Pixelation To Redact Sensitive Information (2022-02-15; mosaic can be undone; cover the text completely with black boxes)
Hyogo Prefecture: "On the leak of personal information in the survey results of community farming organizations" (in Japanese) (announced to the press 2025-12-12, material dated 12-16; data from a pasted chart exposed 600 people)
Windows Insider Blog: New updates for Snipping Tool and Phone Link (2023-09-14; automatic hiding covers emails and phone numbers)
Microsoft Support: Use Snipping Tool to capture screenshots (text is read on the device; checked from a search snippet)
TechSmith: Automatically redact data in screenshots (Snagit Smart Redact) (the 9 kinds it finds; an opaque box is the safest)
TechSmith: Spotlight Tool (Mac) (darkens or blurs everything except the picked part)
App Store: Blur ID - Hide Chat Screenshot (description and price of an app that automatically blurs faces and text in chat screenshots)
@DIME: "Image editing and handwritten signatures, all on one device! What is the little-known iPhone 'Markup' feature?" (in Japanese) (2023-09-03; the article's claim that a marker may show through)
MDN: HTMLCanvasElement: toBlob() method (turns canvas content into an image; PNG by default)
OWASP: Input Validation Cheat Sheet (the weakness of listing dangerous things and blocking them)
MDN: Input validation (deciding what to let through holds up better against things nobody thought of)
PETS 2023: Story Beyond the Eye: Glyph Positions Break PDF Text Redaction (the width and position of a hidden spot leak hints about the text)
Personal Information Protection Commission Q&A Q17-1 (in Japanese) (when mistakenly sending information that includes My Number may constitute a leak)

The prototype built from this research: Show Just This (tap one bubble to show; the rest turns to gray shapes) (it runs on made-up data, and the ZIP is a free download)