Pixelation isn't automatically safe
The common assumption goes: pixel mush over the face = anonymous. That's only conditionally true. Light pixelation or blurring doesn't remove the information, it only spreads it — and from that residual information a rough picture can under some conditions be reconstructed. For a snapshot among friends it may be enough; where protection really matters (license plates, bystanders' faces, sensitive documents), it's the wrong method.
The safe method: an opaque fill
An area only becomes truly safe with a fully opaque, solid fill — a black or colored bar at 100% opacity. Behind it no image information remains in the saved image, so there's nothing to reconstruct. Two conditions must be met:
- Full opacity — no semi-transparent color the original shows through.
- Rendered firmly into the image — after painting over, save the file as a new pixel image (JPG/PNG) so the bar becomes part of the pixels and doesn't stay a movable object.
The PDF and document trap
A particularly dangerous misconception: putting a black bar over text in a PDF or Word document. As long as the bar is an object you can move or delete, the text sits intact underneath — anyone can expose it again. This has led to spectacular data breaches in the past. It only becomes safe once you export the page as a pixel image (or use a real redaction function that deletes the content) and build a new document from it.
The often-forgotten second step: metadata
Even a perfectly blacked-out face helps little if the file keeps talking in the background: EXIF data often contains GPS location, capture time, and device. Anonymize a photo and then share it with location, and you've done only half the job. So after redacting, run it once through the metadata editor — it shows what's inside and removes it browser-local, without uploading the image.
How to do it in practice
- Paint over the area opaquely. On a phone with the markup pen (iPhone: Edit → Markup; Android: Google Photos → Markup), full opacity. On a computer with any image editor that can fill a rectangle.
- Save as a new file (JPG or PNG) so the fill is burned in.
- Remove metadata with the metadata tool.
- Sanity check: look at the finished image — is the license plate reflected somewhere in the paintwork? Is the face visible again in a window pane in the background? Such side channels are easily overlooked.
When redacting is needed at all
It becomes legally relevant as soon as recognizable people are involved: on publicly shared photos, bystanders have a right to their own image. What's allowed and what needs consent — especially at events and with children — is covered in a dedicated article on the right to one's own image and publishing event photos.
Frequently asked questions
Is pixelation safe for making faces unrecognizable?
Only if it's strong enough. Light pixelation or blurring can under some conditions be partially reconstructed, because residual information still sits in the image. Truly safe is an opaque, solid fill (a black or colored bar) over the area — behind it no image information remains.
Is putting a black bar over text enough?
Only if the bar is rendered firmly into the image and the file is re-saved afterward. In PDFs or documents where the bar stays a movable object, it can be removed and the text is back. On pixel images (JPG/PNG) a burned-in opaque bar is safe.
Is there anything else to consider after redacting?
Yes — the metadata. A photo whose faces you've blacked out can still reveal GPS location, capture time, and device in the EXIF data. So remove the metadata before sharing too.
How do I quickly redact something on a phone?
iPhone: Photo → Edit → Markup pen, paint over the area with an opaque pen or the rectangle shape. Android (Google Photos): Edit → Markup. What matters is full opacity, no semi-transparent color, and then save as a new file.
Sources
Apple — Markup on iPhone · GDPR — General Data Protection Regulation.