Blur a face in a photo

Why people blur faces before posting

Most of the time it is not about the person holding the camera. It is the four strangers behind them. A photo from a conference, a school pickup, a protest, or a busy street puts people in your frame who never agreed to appear on your feed. Covering them is the difference between posting a picture of your day and publishing a picture of theirs.

The other common case is a photo you have to send but cannot send as-is: an ID badge for a support ticket, a delivery confirmation with someone at the door, a group screenshot where one person asked to be left out. In those, the face is incidental to the reason you are sharing, so covering it costs you nothing.

Where automatic face detection falls down

Find faces uses a detection model that looks for front-facing, roughly upright faces at a reasonable size in the frame. It is genuinely good at that and genuinely bad at everything else. Expect it to miss:

• Faces in profile, or turned more than about forty-five degrees.
• Faces that are small in the frame, like people at the back of a crowd shot.
• Faces partly covered by a mask, a hood, sunglasses, or someone else in front of them.
• Faces in a reflection, on a screen inside your photo, or on a poster on the wall behind you.
• Faces at an angle, like a photo taken looking down at a table.

Treat the suggestions as a first pass, not a guarantee. The habit worth building is simple: count the people you can see in the photo, then count the boxes you placed. If those two numbers disagree, find out why before you download.

Cover the head, not just the eyes

A black bar across the eyes is a magazine convention, not a privacy measure. Hair, jawline, glasses, an earring, a distinctive beard, and the shirt collar underneath all narrow the field enormously, especially for anyone who already knows the person. If the goal is that a colleague scrolling past does not recognise their neighbour, cover the whole head with a little padding.

The same goes for context around the face. A name badge two inches below the chin undoes a perfect blur. So does a reflection in the window behind them.

Blur strength matters more than people expect

A soft blur that still leaves a recognisable head shape is decoration. Research on de-blurring has repeatedly shown that weak blur and small mosaic tiles can be partly reversed, particularly when the attacker has a set of candidate photos to match against. That is a real scenario for anyone in a school group, a small company, or a local community.

Push the blur hard enough that you cannot tell who it is when you look at your own export at full size. If you can still tell, so can someone who knows them. When identification would genuinely harm someone, skip blur entirely and place a solid black bar over the head. It is uglier and it is final.

Check the export, not the preview

Download the PNG and open it before you send it. Two things go wrong at this step. The first is a box that looks like it covers the face in a small preview but leaves an ear or a chin outside it at full resolution. The second is sending the original by accident, because it is still the most recent file in your camera roll and the redacted one sorted somewhere else.

Save as PNG rather than JPEG. Chat apps recompress what you send, and JPEG artefacts around a hard-edged bar can hint at the shape of what is underneath. More on why PNG is the safer export.