Anonymity is three separate problems
The first is who is visible. Faces are the obvious part, and the ones people remember to deal with.
The second is what sits at the edge of the frame — a street sign, a door number, paperwork on a desk, a view out of a window. Cropping is often the fastest fix and the one most often skipped.
The third is the block of data written into the file itself: coordinates, camera serial number, timestamps, sometimes an owner name. None of it is visible in the picture, and all of it travels with the file.
The serial number problem
The one that surprises people is the camera serial. It is identical in every photo that camera takes, so a photo posted anonymously and a photo published under your own name can be tied together by a number neither of them displays.
Nothing about cropping or covering faces touches it. It only goes when the file is rebuilt.
What this cannot do for you
It cannot know that the jacket in the photo is recognisable to the people you are hiding from, or that the room is identifiable to anyone who has been in it. It covers what you tell it to cover, plus the faces it can find.
If the stakes are high — reporting, safety, anything where being wrong has consequences — treat the automatic face detection as a starting point rather than a guarantee, and check the exported file yourself before it goes anywhere.
Questions
- Is a screenshot enough to anonymize a photo?
- A screenshot drops the metadata, because it produces a new file. It does nothing about faces or anything else visible in the frame, and it costs you image quality.
- Does this work offline?
- Yes. Once the page has loaded you can disconnect entirely and everything still works, because none of it needed a server in the first place.
- What is left in the exported file?
- The pixels, and the minimum structure a JPEG, PNG or WEBP needs to be readable. No location, camera, timestamps, serial numbers, owner names or embedded thumbnails.
- Can I check the result myself?
- Yes, and you should. Open the downloaded file in any metadata viewer, or run exiftool against it, and compare against the original.