Hide sensitive details so they stay hidden.

Blurring and pixelating both work by throwing away detail, but not always enough of it. A light Gaussian blur is mathematically reversible in principle: because it spreads each pixel's value in a known way, software can sometimes sharpen it back toward the original, especially for text. Coarse pixelation is worse for structured content — a pixelated licence plate or a short PIN has so few possibilities that they can be reconstructed by testing which original would blur to what you see.

The lesson is not to abandon blur and pixelation, but to use them aggressively. Redaction that removes a little detail is decoration; redaction that removes almost all of it is protection. For anything truly sensitive — a signature, an account number, a face you must protect — the safest approach is to obliterate the region entirely rather than merely soften it.

Three rules make redaction reliable. First, be heavy-handed: use a strong blur radius or a very coarse pixelation, or better still, cover truly critical data with a solid opaque block that removes the information completely rather than transforming it. Second, size the redacted area generously — extend it past the edges of the text or face so no readable fragments peek out around the border.

Third, and most important, flatten and re-export. The redaction must become part of the actual pixels of a new image file. If you send the original file with a blur applied as a separate, editable layer or as a non-destructive filter, the recipient's software may let them simply switch it off. Exporting a fresh JPG or PNG bakes the redaction in permanently — there is no layer to peel back because the underlying pixels are gone.

You can blur a face perfectly and still give away exactly where the photo was taken. Digital photos, especially from phones, carry embedded metadata (EXIF) that can include GPS coordinates, the date and time, the device, and sometimes even the owner's name. None of that is visible in the picture, and none of it is affected by blurring the image — it rides along inside the file.

So redaction has two halves: hide the visible detail, and strip the invisible detail. Before you publish a photo where location or identity matters, remove its metadata as well as its sensitive pixels. Many tools that re-export an image will drop most metadata in the process, but it is worth confirming — a screenshot of a photo, for instance, removes the original EXIF, whereas a direct edit may preserve it. Treat the metadata as part of what you are redacting.