How to Redact an Image: Black Out or Blur the Right Way
Blurring a face or pixelating a name feels safe. Often it isn't — both can be reversed. Here's how to hide something in a photo so it genuinely cannot be recovered.
You want to post a photo but hide one thing in it — a face, a house number, an email on a screen, a licence plate. So you reach for the blur tool, smudge it out, and share it. Done, right?
Not necessarily. The most common ways people hide things in images are also the easiest to undo. Before you rely on one, it is worth knowing which methods actually destroy the information and which only disguise it.
The Three Ways People Hide Things — Ranked
| Method | How safe is it? |
|---|---|
| Black box | Safe. The pixels are replaced with solid colour — there is nothing left underneath to recover. |
| Pixelate | Risky. Blocky, but the original detail is averaged, not destroyed — and for predictable content it can be partially reversed. |
| Blur | Risky. A blur is a reversible mathematical filter; with the right technique, blurred text and faces can sometimes be reconstructed. |
Why blur and pixelate can be undone
A blur spreads each pixel's value across its neighbours in a known, mathematical way. Because the operation is predictable, it can be run in reverse to approximate the original — this is a well-documented class of attack, and tools exist that recover text from blurred or pixelated screenshots. Pixelation is weaker than it looks for the same reason: when the hidden content is from a small, predictable set — digits, letters in a known font, a licence plate format — an attacker can pixelate every candidate the same way and match the blocks, reconstructing the original. The famous cases of "unredacted" pixelated documents were undone exactly like this.
None of that is possible with a solid black box, because a black box does not transform the pixels — it replaces them. There is no original signal left to recover.
Rule of thumb: if what you are hiding is sensitive, or if it is text, numbers, or a face an adversary might try to reconstruct, use a black box. Reserve pixelation for casual, low-stakes cases where you just want to de-emphasise something.
The Overlay Trap (and the Metadata You Forgot)
There is a second, quieter failure. In some editors, drawing a shape over part of an image adds a layer on top rather than changing the picture itself. If you then save to a layered format — or the tool keeps an editable history — the original can resurface. A redaction only counts when it is flattened into the final pixels of a single-layer image.
And remember the file carries more than the picture: a photo straight from a camera still holds its EXIF metadata, including the GPS location where it was taken. Hiding a face in the frame does nothing about the coordinates in the file.
How to Redact an Image Properly
- Use a black box for anything sensitive. It is the only method with no path back to the original.
- Cover generously. Leave no sliver of the detail — a half-visible digit or the edge of a face is often enough to reconstruct the rest.
- Flatten to a single image. Export a normal JPEG or PNG so there are no layers and no editable overlay — just final pixels.
- Strip the metadata. Make sure the export does not carry the original EXIF/GPS.
- Do it without uploading. The photo you are redacting is, by definition, one you do not want seen — so it should not be sent to a stranger's server to be edited.
RedactLocal's Image Redactor does all of this in your browser. Drag a black box (or pixelate, if you prefer) over anything you want gone; it is burned into the pixels at full resolution, the image is re-encoded from scratch so no original data or metadata survives, and the file never leaves your device.
What About Faces Specifically?
For true anonymity — a protest photo, a witness, a child — use a black box over the whole face, not a blur or a small pixel patch. Blurred and lightly pixelated faces have been re-identified by both reconstruction techniques and plain facial-recognition matching. If the stakes are real, destroy the pixels; don't disguise them.
Redacting a screenshot rather than a photo? The failure modes are a little different — your phone's crop-and-markup tool can quietly leave the original behind. How to redact a screenshot before you share it covers those specifics.
This guide is for general privacy information. Whether a given redaction is "enough" depends on what you are hiding and from whom. When it truly matters, prefer the method that removes information outright — a solid black box on a flattened image — over any method that merely obscures it.
Hide It for Good, Not Just for Show
Black out or pixelate anything in a photo — burned into the pixels, metadata stripped, with the image never leaving your browser.
Open the Image Redactor