Blur or pixelate: which actually hides a face?
Use strong settings. Light blur and small pixel blocks can sometimes be partly reversed or recognised, especially for text such as licence plates. Large pixel blocks (a face covered by only a few blocks across) or heavy blur remove the detail for real. For documents with sensitive numbers, a solid block is safest: use the pixelate mode at its maximum strength.
Privately, on your device
Blurring is done with your browser’s canvas. The photo is never uploaded, which matters when the reason you are blurring is privacy.
Questions
Is blurring a face permanent?
Yes, in the downloaded file. The original pixels are replaced. Keep your original if you might need it.
Can I blur a licence plate?
Yes. Use pixelate at high strength so the characters are fully destroyed, not just softened.
Can I blur faces in a video?
Yes. In the video watermark remover, draw a box and choose blur or pixelate for it. It works well for static shots.