Short answer: macOS Markup has no blur tool — and a hand-drawn rectangle is easy to get wrong. Lovely Screenshots (free) has proper Blur and Pixelate tools: drag a box over the secret, export, and the data is gone from the shared file's pixels.
Why this matters more than it seems
Screenshots leak things: email addresses in a bug report, an API key in a terminal, a customer's name in a CRM, your home address in a maps tab. Once a shot is posted to Slack or a public issue, you can't un-share it. Redacting before sharing needs to be a two-second habit, which means the tool has to be right there in your capture flow.
Blur and pixelate in Lovely Screenshots
- Capture and open the editor. Take a screenshot with Lovely (⌘⇧4 area or any other mode) and click the pencil on the preview card — or drop any existing image into the editor.
- Blur or pixelate the sensitive part. Press X for Pixelate or pick Blur from the toolbar, then drag a box over the email address, API key, card number or face. The effect samples the real pixels underneath, so it moves with the region if you adjust it.
- Check the edges. Zoom in (trackpad pinch or ⌘+) and make sure the whole string is covered — including any place it repeats elsewhere in the shot. Add a second box wherever needed.
- Export. Hit Copy or Save. The exported PNG has the redaction baked into the pixels — the original data is not recoverable from the file.
Frequently asked questions
Can macOS Markup blur a screenshot?
No — Preview/Markup offers shapes and text but no blur or pixelate. The common workaround is drawing a black rectangle, which works only if the rectangle is fully opaque; semi-transparent highlights over text can often be read straight through or recovered by boosting contrast.
Blur or pixelate — which is safer?
For text secrets (keys, passwords, card numbers), pixelate with a coarse block size or a heavy blur radius. Light blurs on short, known-format strings can sometimes be reversed by comparison attacks. When in doubt, make it chunkier — or cover it entirely.
Is the hidden data really gone from the exported file?
Yes. Lovely bakes the effect into the exported image's pixels. (Inside Lovely, your own edit session stays re-editable on your Mac — but the PNG you share carries only the redacted pixels.)
Is this free?
Yes — the full annotation editor, including blur and pixelate, is free in Lovely Screenshots.