This is why with redact.photo I randomly shuffle the pixels before blurring so it looks like you can reverse engineer it but you’ll just get scrambled pixels.
I thought that blurring a photo would set each pixel to the average color value of all its neighbors. Since information is lost, how could you reverse engineer a blurred photo?
If there are a limited number of input permutations then you can test all of them to see which is plausible.
Hah.. but by shuffling you preserve the number of white and black pixels, which may make it possible to reverse ;)