How to redact a screenshot on Mac, and why blur isn’t enough

Before you send a screenshot, the e-mail addresses, card numbers, passwords and names on it should go. Here are three ways to do it on a Mac, from the one already installed to the fastest, and what each one leaves behind.

Blur, pixelate or a solid box?

Blur and pixelate make text hard to read for a person, but they keep some of it: the blurred pixels still depend on the letters underneath. Short text with few possibilities, like a card number, a PIN or a code, can sometimes be guessed back by trying every value and comparing the blur. A solid box replaces the pixels, so there is nothing of the original left in the file.

	Blur	Pixelate	Solid box
Looks	Soft, unobtrusive	Blocky	A plain block of colour
What is left of the text	A smeared copy of it	An average of each block	Nothing
Safe for numbers, keys, passwords	No	No	Yes
Good for	Faces and backgrounds you only want to soften	The same	Anything private

1. With Preview, already on your Mac

Open the screenshot in Preview and click the Markup button to show the Markup toolbar.
Choose Shapes, then the rectangle, and set its fill colour to black.
Draw a box over each private detail.
Choose File › Export and save a PNG or JPEG. Don’t save it as a PDF: there the box can stay a separate shape that someone can move away.

This is free and needs nothing new. It is slow for many details, and you have to find each one yourself.

2. With SimpleShot, in one click

Take the screenshot with SimpleShot (⇧⌘4 for an area), or open an existing image in its editor with Open.
Click Hide Sensitive Data. SimpleShot reads the text on your Mac and covers every e-mail address, phone and card number, IBAN, API key, password and IP address it finds with solid pixels. The button shows how many are left.
Cover anything else, such as names or faces, with Secure Redact (D): drag a box over it.
Copy, save or share. The covered pixels are solid in every file, copy and drag.

To have it every time, turn on Settings › Privacy › Hide sensitive data automatically. The original stays in your Library on your Mac, so any cover can be undone in the editor. SimpleShot is free, needs no account and doesn’t upload your screenshots.

Download for Mac

3. In the browser, without installing

Not on your Mac, or just once? Two free tools on this site work in any current browser and don’t upload the image:

Hide personal info on a screenshot finds the same kinds of details as the app and covers them with solid boxes.
Redact a screenshot lets you drag solid boxes over anything you choose.

Which way to choose — honestly

Once in a while, one or two details: Preview is enough.
Screenshots you share every day: SimpleShot finds the details for you, so you don’t miss the one key in the corner.
Another computer: the browser tools.
Names, addresses, faces and handwriting: no tool here finds them by itself. Cover them by hand, and look the image over before you share it.

Questions

How do I blur part of a screenshot on a Mac?

Preview has no blur; draw a filled shape with Markup instead, or use SimpleShot’s Blur (B) or Pixelate (X). For anything private, use a solid box rather than blur: blurred text can sometimes be read back.

Can a redacted screenshot be un-redacted?

A solid box in a PNG or JPEG can’t be: the original pixels are no longer in the file. Blur and pixelate can sometimes be reversed on short text, and a box in a PDF can stay a separate shape that can be removed.

Can SimpleShot find private details by itself?

Yes: e-mail addresses, phone and card numbers, IBANs, API keys and tokens, passwords written after a label, and IP addresses. It reads the text on your Mac; names, addresses and faces you cover by hand.

Is my screenshot sent anywhere?

No. Preview and SimpleShot work on your Mac, and the browser tools on this site read the image in the tab without uploading it. With SimpleShot, a capture leaves your Mac only if you make a link to it.

Redact while you capture,
on your Mac.