Is my photo uploaded to detect the faces?
No. The face detector is a small AI model that loads into your browser and runs on your device - the photo itself never leaves your machine. You can disconnect from the internet after the detector loads and it still works.
Should I use blur, pixelate, or blackout?
Pixelate is the best default: a coarse mosaic discards the underlying detail. Blackout is the bluntest and most certain. Gaussian blur looks the most natural, but weak blur on a high-resolution face has been partially reversed in research settings - crank the strength if you use it.
Why didn't it find every face?
The local detector is tuned for clear, reasonably close faces. Turned heads, small faces in crowds, and partly hidden faces can be missed - drag a box over anything it skipped, it takes a second.
Can a blurred face be recovered from the download?
Not from a strong pixelation or a blackout - the pixel information is destroyed and the file is re-encoded with no hidden original inside. The one case to avoid is a very light blur on a large, sharp face.
Does blurring also remove the photo's metadata?
Yes, as a side effect: the output is rebuilt from raw pixels, so EXIF blocks like GPS coordinates and camera model aren't carried over. You can verify by dropping the result into the EXIF Viewer.