But a bad blur doesn't. That's why your parent comment asks what kind of blur they use.
Edit: Turns out it's a 25px Gaussian blur. There's some downsampling beforehand, but not much, and no color discretization. In other words, they use a bad blur, but compensate with a large security margin. I wouldn't be surprised if this was vulnerable to "if I have a thousand photos of faces and I think one of them matches the blurred face, I can figure out which one with high confidence", and they can get basically the same aesthetic effect if they heavily pixelate and discretize colors before blurring.
> "if I have a thousand photos of faces and I think one of them matches the blurred face, I can figure out which one with high confidence",
Is that actually a practical attack here? I can see it working if you have 1000 passport photo or mugshot frames photos, and a blurred photo with the same level/front-on framing. But is there a practical attack for non direct-facing-camera blurred pictures? (Assuming the scale of "locals at a local protest" instead of "Find Edward Snowden's blurred face from any BLM protest, no matter what the cost!!!")
Good point, I'd be surprised if lighting and orientation doesn't overwhelm all other information at this level of blur.
But I've been surprised by impressive digital forensics before—what if you can determine lighting and orientation from the rest of the photo, and then simulate them on each passport photo/mugshot? I'd still feel much more comfortable if they pixelized and color-discretized before blurring, and I still think the aesthetic effect would be much the same.
Edit: Turns out it's a 25px Gaussian blur. There's some downsampling beforehand, but not much, and no color discretization. In other words, they use a bad blur, but compensate with a large security margin. I wouldn't be surprised if this was vulnerable to "if I have a thousand photos of faces and I think one of them matches the blurred face, I can figure out which one with high confidence", and they can get basically the same aesthetic effect if they heavily pixelate and discretize colors before blurring.
https://news.ycombinator.com/item?id=23415600