How to redact sensitive info in screenshots — without uploading them

You need to share a screenshot of a receipt, an error message, or a support ticket — and buried somewhere in the frame is an email address, an order ID, a balance, or half a password. The instinct is to grab an online blur tool. The problem: uploading a sensitive image to a website in order to redact the sensitive parts means handing the unredacted original to that website's servers, its logs, and whoever comes after them. Redaction in the cloud defeats the purpose of redaction.

The alternative is a local redaction workflow: the image is captured, edited, and exported on your own machine, and the only copy that ever leaves it is the final, already-redacted file you deliberately send. That's exactly what this tutorial walks through, using SnapLocal, a free private screenshot tool for Chrome whose mosaic redactor costs nothing and whose manifest contains no permissions to contact any server.

Why “redact locally” beats “redact online”

• The original never exists on someone else's disk. Cloud editors must receive the full-resolution, unredacted image. Even if it's “deleted after processing,” it passed through infrastructure you don't control — and possibly their analytics, backups, and error logs.
• No account, no email, no fingerprint. Online tools routinely gate exports behind sign-ups. A local tool needs none of that.
• It works offline. On a plane, behind a corporate proxy, or on a locked-down machine — a local workflow doesn't care about your network conditions.
• Redaction you can trust. Proper mosaic is pixel-destructive: the original data is replaced, not hidden behind a translucent layer that a recipient could peel off in an image editor.

The 6-step local redaction workflow

1. Capture only what you need

   Press Alt+Shift+S and drag a tight region around the content you actually want to share. Every pixel you exclude is a pixel you don't have to redact later — the cheapest form of screenshot redaction is never capturing the secret in the first place. SnapLocal's capture runs entirely on-device; the image is written straight to chrome.storage.local, so there's no “uploading…” step to wait for and nothing to intercept.

2. Mosaic everything sensitive — free, unlimited

   Pick the mosaic tool and drag over each sensitive element: names, emails, phone numbers, IDs, balances, QR codes, avatars, URLs with tokens in them. Adjust the brush size so the mosaic comfortably covers more than the visible text — assume an attacker knows the approximate shape of what's underneath. In SnapLocal the mosaic tool is free in the base tier, with no watermark and no usage cap. (In Nimbus, the equivalent functionality sits behind a paywall of roughly $60/year — redaction shouldn't be a premium feature.)

3. Crop away the edges

   Sensitive data loves the periphery: browser URL bars with session tokens, bookmark bars revealing your bank, notification toasts in the corner, taskbar app lists. Re-crop the capture tightly, or simply capture a smaller region in step 1. If a whole section of the screen is irrelevant — a sidebar, a tab strip — cropping it out is stronger than mosaicking it, because deleted pixels can't be recovered at all.

4. Check the background, not just the foreground

   Zoom in and scan the entire frame once more. The classic misses: faint placeholder text behind semi-transparent overlays, reflection of the screen in a glossy surface within the shot, file paths in a terminal prompt, partial characters at the very edge of a mosaic patch, and EXIF-style context you can't see but recipients can infer (a username in a window title). A slow left-to-right, top-to-bottom sweep catches almost everything.

5. Verify the redaction is destructive

   Mosaic must replace pixels, not overlay them. A quick sanity check before you export: if the redacted area still shows any recognizable outline of the original text at full zoom, mosaic harder or make the patch bigger. SnapLocal's mosaic rasterizes the region into anonymized blocks at edit time — the original pixels are gone from the exported file, not hidden beneath a sticker.

6. Export locally, share deliberately

   Export to PNG or JPG (both free, no watermark), or copy straight to the clipboard and paste into your ticket, doc, or chat. The key property: the first network hop this image ever makes is the one you chose — attaching it to the message you're sending. No intermediate server ever held the unredacted original, because there was no intermediate server.

Common redaction mistakes (and how to avoid them)

• Translucent “blur” that isn't. A soft blur or a semi-transparent box over short text can sometimes be defeated by contrast adjustment or OCR. Use a real mosaic with generous coverage.
• Redacting after uploading. If the workflow is “capture → share link → edit the online copy,” the unredacted original is already on the server. Always redact before the image leaves your machine. This is the exact trap of upload-by-default tools — see our breakdown of where Lightshot's screenshots actually go.
• Forgetting the capture history. Editing tools that sync history to the cloud keep every earlier, unredacted version. SnapLocal's history is local-only (last 20 captures free, unlimited with Pro) and can be cleared in one click.
• One-pass complacency. Do the background sweep as a separate pass from the mosaic pass. Different eyes, different catches — even when both passes are yours.

What if you don't use a Chrome extension?

The same principles work with any local tool: the built-in screenshot utilities on Windows, macOS, and Linux all keep captures on-device, and you can redact in a local image editor afterwards. The trade-off is friction — two apps, several save-and-reopen cycles, and editors that charge for export. A browser extension that combines capture and a free mosaic in one place is simply the fast lane of the same local workflow. For a full category comparison, read our roundup of the best private screenshot tools for Chrome in 2026, which grades each tool on upload behavior and price.