Blur vs. Redact: How to Hide Sensitive Information in an Image Without Leaking It
By the Super Simple Digital Tools Team · Updated June 2026
Most people blur a photo by instinct: there is a face, a plate, or an account number they would rather not broadcast, so they smear it and hit share. That instinct is right, but the execution often is not. Blurring and pixelation look final to the eye while quietly preserving a mathematical trace of what was underneath, and a growing set of tools can read that trace back out. Understanding the difference between hiding something visually and removing it permanently is the whole game when you are protecting real secrets.
Here is why blur leaks. A blur replaces each pixel with a weighted average of its neighbors; pixelation replaces a square block of pixels with one averaged color. Neither throws information away cleanly. Researchers at Bishop Fox demonstrated this with Unredacter, an improvement on the earlier Depix tool: it walks through possible characters, renders each in the same font and size, pixelates that guess, and compares it to the redacted area until the math lines up. Short, predictable strings such as card numbers, dates, or check fields are the easiest to recover because there are so few plausible permutations.
That does not make blur useless. For low-stakes clutter, blur is perfectly reasonable: a stranger's face in the background of a vacation photo, a street sign, a messy desk behind your video call, or a neighbor's car in a real-estate listing. The goal there is courtesy and reducing incidental identifiability, not defeating a determined attacker with a depixelation script. A strong Gaussian blur of 30 pixels or more, or a coarse pixelation, comfortably handles those cases and keeps the picture looking natural.
When the content actually matters, switch tactics. Passwords, government ID numbers, bank details, API keys, signatures, and anything you would be harmed by losing should be covered with a solid, opaque block, not a blur. A solid mask leaves no averaged pixels to reconstruct, which is why every redaction guide lands on the same advice: black bars, nothing fancier. Draw the block generously so it overhangs the text on every side; partial letters or a stray digit poking out can be enough for a reconstruction tool, or a sharp-eyed human, to fill in the rest.
Finally, mind the export and the original. Because this tool processes images in your browser, your file stays on your device, but you still need to save the flattened output, the version with the obscuring baked into the pixels, and share only that. Never send the unedited original, and remember that screenshots of formatted documents can hide text under matching colors that copies right back out. Blur for tidiness, mask for secrets, double-check the exported file, and you will share photos without sharing what you meant to keep.
- For passwords, ID numbers, or card details, choose the solid-block mode, not blur or pixelate, then make the block extend past the text on all four sides.
- When blurring faces or license plates for privacy, push the blur strength to 30 pixels or higher so no feature or character stays legible.
- Always export and share the flattened PNG or JPEG, and keep the unedited original off-line so you never accidentally post the version without redactions.
- Zoom in before exporting and check that no partial letters, digits, or reflections peek out from the edges of the blurred or masked region.