---
title: "How to redact a screenshot on Mac before you send it to an AI agent"
description: "What to hide in a screenshot before Claude Code, Codex or ChatGPT reads it, why blur and pixelation are not always enough, and how to redact properly on macOS."
url: https://www.bigshot.pics/blog/redact-screenshot-mac
---
# How to redact a screenshot on Mac before you send it to an AI agent

*2026-10-07*


A screenshot of a bug often shows more than the bug: a customer's email in a
table, an API key on a settings page, a name in a chat sidebar. Once an agent
has read the image, that text is part of the conversation, and models read
text in screenshots very well. Redact before you share, not after.

## What to look for

Before a screenshot goes to an agent, scan it for:

- **Credentials.** API keys, tokens, passwords, connection strings, an `.env`
  file open in the editor, terminal output that prints secrets.
- **Personal data.** Names, email addresses, phone numbers, addresses,
  payment details, including test data that looks real.
- **Other people's messages.** Chat and email sidebars that happen to be on
  screen.
- **Internal details.** Admin URLs, account IDs and hostnames you would not
  paste into a public issue.

## The safest redaction is not capturing it

Crop it out, or capture less to begin with: one window instead of the whole
screen, one panel instead of the window. Nothing in the image means nothing
to recover.

## Blur and pixelation: good for names, not for secrets

Blurring or pixelating text makes it unreadable to a person, but it does not
always destroy it. Researchers have reconstructed pixelated text by
pixelating guesses the same way and comparing the blocks; the open-source
tool Depix is the best-known example. It works best on small block sizes and
plain fonts, which is exactly what UI text is.

So:

| What is in the screenshot | Do this |
|---|---|
| A password, key or token | Crop it out. Then rotate it anyway if it was on screen in a shared capture. |
| Card numbers, government IDs | Crop out, or cover with a solid opaque box |
| Names, emails, addresses in a list | Pixelate or blur with a large block size |
| Faces and avatars | Pixelate or blur |

A solid box must replace the pixels, not sit on top of them. In a PDF, a
drawn rectangle is often a separate layer that can be moved or deleted. In a
PNG saved from an image editor, it becomes part of the image. Reopen the file
and check before you share it.

## Redacting in Preview

macOS Preview can do a solid box: open the screenshot, click the Markup
button, draw a rectangle, and set its fill colour to black in the shape
style controls. Save, close, and reopen to confirm the area is covered.

## Redacting in Bigshot

In [Bigshot](https://www.bigshot.pics/)'s editor, press **B** for Redact and drag over anything that
should not be readable. Redactions pixelate by default; switch to blur in
Settings › General. When you save, the redaction is written into the image,
and Live Text (and Bigshot's own text recognition) cannot read text under it.

![Bigshot's Redact tool: the fields of a checkout form pixelated in place.](https://www.bigshot.pics/screenshots/tool-redact-tile.webp)

For secrets, use the Crop tool (**C**) instead and cut them out of the frame.

## When screenshots go to agents automatically

If your screenshots are saved where an agent can read them, the order of
operations matters. In Bigshot, a Project's screenshot sharing can be:

| Sharing | When the agent can see a capture |
|---|---|
| Automatic | As soon as it is taken |
| Review first | Only after you approve it with **Share now** |
| Off | Never |

With **Automatic**, a capture is listed for agents before you have had a
chance to redact it. In a repository where screenshots often contain
customer data, use **Review first**: capture, redact, save, then approve. An
edited capture needs approval again, so a changed image never reaches an
agent without you seeing it. **Exclude** keeps a capture from agents for good.

These are conventions for finding files, not a security boundary: anything
with access to the folder can read it. See
[Let your agent find your screenshots](https://www.bigshot.pics/blog/screenshot-context-in-your-repo).

## If something slipped through

Excluding or deleting a screenshot does not remove it from a conversation
that has already read it, or from a provider's logs. Treat a secret that
reached an agent as exposed: rotate the key, change the password.

## Checklist

1. Capture less: one window, one panel.
2. Crop out secrets; do not blur them.
3. Pixelate names and personal data with large blocks.
4. Save, reopen, check.
5. In shared folders, review before sharing.
6. If a secret got out, rotate it.