ClarShot is now on the Chrome Web Store, for Chrome, Brave and Opera too.

Guide

How to hide private information in a screenshot, and why blur is not enough

The short answer

Cover it with a solid box you cannot see through, not blur or pixelation, then save it as a new PNG or JPEG. Blur and pixelation leave enough behind for free tools to read the text back. A PDF or an editor's own file can keep the original under your box, so send a plain image.

On a phone? The ClarShot steps below are for a computer: ClarShot runs in Chrome and Edge on Windows, Mac, Linux and ChromeOS.

Why blur and pixelate are not enough

Blur and pixelate do not remove text. They average it. Each block of a pixelated area is the average colour of the pixels that were underneath, so the block still depends on exactly what was written there.

That is enough to get it back. If someone can guess the font and the size, which a screenshot of a known app usually gives away, they can draw every likely word or number the same way, pixelate each one the same way, and keep the one whose blocks match. Security researchers have published tools that do exactly this: Bishop Fox released Unredacter in 2022, after an earlier tool called Depix recovered passwords from pixelated screenshots. Their conclusion is the same as ours: to hide text, use an opaque block.

Try it yourself

The demo below runs in this page and has two steps. In "1. Cover it", drag over the table. In "2. Try to break it", your browser hides a random 4-digit code and tries all 10,000 possibilities. Pixelate and blur give it away within seconds. Solid does not.

Drag over the demo table to cover what should stay private, then download the PNG. Every name and email in it is fictional.

Without installing anything

Any image editor can hide text safely, as long as you do three things:

  1. Use a filled rectangle, not a blur. Draw an opaque box in a solid colour over the text. Black is common; any solid colour works if it is fully opaque.
  2. Export a new flat image. Save as a new PNG or JPEG. Formats that keep layers or annotations, such as an editor's own project format or a PDF with a comment box on top, can keep the original under your box, where anyone can move it aside.
  3. Keep your tools up to date. In 2023, bugs in two widely used screenshot editors, one on phones and one on desktops, left the uncropped original inside edited images saved over the old file. Saving to a new file and updating the editor avoids this kind of problem.

Not sure about a file you already have? Our free screenshot privacy check looks for data after the end of the picture, location and author fields, and pixelated areas, in your browser, without uploading the image.

With ClarShot

ClarShot's editor has three ways to hide a region: Solid, Blur and Pixelate. Solid is the default for new regions, and it is the only irreversible one.

  1. Capture the page or the area you need.
  2. In the editor, choose the hide tool (its button says Blur). It covers with Solid unless you change it.
  3. Drag over each name, email or number. Crop afterwards if you want a smaller image.
  4. Download or copy. The block is burned into the exported file: it is pixels, not a layer on top.
Four rows of an invoice table with the customer names and emails readable
As captured
The same rows in the exported PNG: the customer names and emails replaced by solid blocks
As exported, with Solid

A blur or pixelate box drawn on top of a Solid box stays black in the export, so a later edit cannot bring the text back. And since ClarShot makes no network requests, the uncovered original is never sent anywhere while you work on it.

A checklist before you share

  • Names, email addresses and phone numbers, including in sidebars and avatars.
  • Card numbers, IBANs, amounts and order or invoice numbers.
  • Passwords, API keys, tokens and anything that looks like a long random string.
  • The address bar and the tab titles, which often carry names or IDs.
  • Notifications and message previews that happened to be on screen.

Common questions

Is a black box always safe?

It is safe when it is part of the image itself, in a flat PNG or JPEG. It is not safe when it is a shape on top of the original in a document that keeps both, such as a PDF with an annotation box.

Is blur fine for anything?

For making something less noticeable, yes. For anything that must not be read, no. Treat blur and pixelate as cosmetic.

Can ClarShot find private data for me?

Not yet. A feature called Find, which will point out email addresses, phone numbers, card numbers and IBANs for you to review, is coming, and it will be free. Today you cover them yourself with Solid.

Try it in ClarShotFree, no account, and nothing you capture leaves your computer.
Add to Chrome

ClarShot works in Chrome and Edge on a computer, not on phones. Send yourself the link and open it there.