How to blur sensitive data in a screenshot

Updated 1 September 2026

Before the how: blur and pixelation are not reliable redaction. Both are reversible in principle, and pixelated text has been recovered in practice more than once — the transformation is deterministic, so an attacker who can guess the font and the original text can search for a pixelation that matches.

For anything that matters — credentials, account numbers, names, addresses — use a solid opaque shape. Blur is fine for making a screenshot look tidy. It is not a security control.

The free way: Preview

Open the screenshot in Preview
Show the markup toolbar (⇧⌘A)
Choose the Rectangle shape
Draw it over the sensitive area
Set both fill and border to solid black — the fill dropdown defaults to none, which leaves an outlined but perfectly readable box
File → Export as a new file

Two things people get wrong here:

Export, don’t just save. If you save over the original you’ve destroyed the unredacted copy you might need later.

Flatten it. A PDF export can keep the rectangle as a separate movable object sitting on top of readable text. Exporting to PNG or JPEG flattens everything into pixels, which is what you want.

The instant way: Quick Look markup

Select the file in Finder, press Space, click the markup icon, draw a filled rectangle. Same tools, fewer clicks, and it edits the original in place — so duplicate the file first (⌘D).

Doing it in bulk

If you redact the same regions repeatedly — a sidebar with a client name, a header with an account number — Preview gets tedious quickly.

Tools that handle this better: CleanShot X has blur and highlight in its editor and can detect some sensitive values automatically. Screenshot Inbox flags API-key-shaped strings and email addresses when it reads a capture and can turn those findings into redaction regions in one click, with saved recipes for regions you apply often. Both write a separate file rather than modifying the original.

What people forget to redact

The thing you’re pointing at is rarely the leak. The leak is somewhere else in the frame:

The browser URL bar — often contains a customer id, an account slug or a session token
Browser tabs — tab titles name the other client you’re working with
The window title — “Acme Corp — Admin” in a screenshot you’re posting to a public issue
Notification banners that arrived mid-capture
The Dock and the menu bar — reveals more than you’d think
Autocomplete dropdowns showing previous entries
The clock, if when you were working is sensitive
Sidebars and account switchers listing every organisation you have access to
Test data that isn’t test data — staging environments seeded from production

Metadata

Screenshots carry EXIF metadata: dimensions, creation time, sometimes the software used. Rarely sensitive, occasionally relevant if the timestamp matters.

To strip it:

mogrify -strip screenshot.png

(needs ImageMagick, brew install imagemagick)

Note that redacting pixels does nothing to metadata, and stripping metadata does nothing to pixels. They’re separate problems.

A checklist before posting publicly

Look at the whole image, not the part you’re pointing at
Check the URL bar, tab titles and window title
Use solid shapes, not blur, for anything that matters
Export to PNG so it’s flattened
Open the exported file and look at it again
Ask whether the structure leaks anything — an internal URL scheme, an id format, a staging hostname

Step 5 is the one that catches real mistakes. Look at the file you’re about to upload, not the editor you made it in.