Guide
How to blur sensitive information in a screenshot on a Mac
Most leaked secrets in screenshots were not in the part the sender was looking at. This guide covers the tools macOS gives you, the safe way to redact, and a checklist to run before you hit send.
Blur is not always redaction
A light Gaussian blur over text in a known font can sometimes be reconstructed, because the blur is a predictable transform. Coarse pixelation destroys more information, and an opaque shape destroys all of it. For anything that matters, such as keys, tokens, or account numbers, use coarse pixelation or a solid box, and crop it out entirely when you can.
Method 1: Markup in Preview or the ⌘⇧5 thumbnail
- Take the screenshot, then click the floating thumbnail, or open the file in Preview and click the Markup toolbar button.
- Choose Shapes, pick the rectangle, and drag it over the sensitive area.
- Set the fill color to a solid color and make sure the shape is fully opaque.
- Save. Check the result at full size before sharing.
Note. Markup has no blur or pixelate tool. An opaque rectangle is the only safe option, and a semi-transparent one is not safe at all.
Method 2: Blur or pixelate in the Shotnix editor
- Take the capture and press ⌘E on the overlay to open the editor.
- Choose Blur or Pixelate and drag over the area. Use Pixelate at a coarse size for text.
- For absolute certainty, draw a filled rectangle over the area instead.
- Press ⌘C to copy or ⌘S to save. The redaction is baked into the exported pixels.
Method 3: Redacting inside a screen recording
For video, the Shotnix demo editor has a Redact effect that is fully opaque in exports, with hard on and off points on the timeline. Use it to cover a notification or a sidebar for part of a recording.
Checklist before you share
- Browser tabs: titles often contain names, ticket numbers, or document titles.
- The URL bar: query strings and IDs.
- Notifications and the menu bar: calendar events, message previews, account names.
- Autocomplete and recent items in dropdowns and search fields.
- Second monitor and background windows if you captured a whole display.
- Terminal history and environment variables in scrollback.
Questions
Can blurred text be recovered?
Sometimes, if the blur is light and the font is known. Use coarse pixelation or an opaque shape for anything sensitive.
Does macOS Markup have a blur tool?
No. Markup offers shapes, text, and signatures. Use an opaque filled rectangle, or a third-party editor with blur and pixelate.
Is pixelation safe?
Coarse pixelation over a small region is generally safe. Fine pixelation over long text is weaker. When in doubt, cover with a solid shape.
Does the exported image keep the original pixels under the blur?
No. In Shotnix the blur, pixelation, or shape is rendered into the exported PNG, JPEG, or WebP. There is no hidden layer to remove.
Try it on your own screen.
Shotnix is free, open source, and local. Download the notarized DMG, or star the repository if you want to follow along.
8.4 MB · macOS 13+ · signed and notarized by Apple · MIT license