What to cover
Screenshots of terminals, dashboards and settings pages often show more than your question needs: API keys and tokens, passwords, e-mail addresses, customer names, internal addresses. Whatever you paste into a chat may be kept with the conversation, so cover these first. The AI can still read the rest of the screenshot.
From screenshot to chat
Take the screenshot and paste it here: the Redact tool is already open. Drag a box over each secret; you can move and resize boxes, and Ctrl+Z or Cmd+Z undoes. Then press Copy PNG and paste the image into the chat. The copy is a new PNG with the boxes burned in, so there's no layer anyone could remove.
Use flat boxes for secrets
Solid replaces the area with flat black, so no trace of the text is left in the file. It's free, and it's the mode for passwords, keys and ID numbers. Pixelate and Blur (Pro) replace the pixels in the file with large blocks and noise and look calmer on names in product screenshots; for secrets, use Solid.