My employer makes a tool that does this! It's a screenshot tool we had been using internally for years that we released last year. It takes a sample of the colors in the image and uses them for random-looking obfuscation. So it's obvious that the data is hidden, but there's no pattern or way to un-blur that data. It doesn't work as well on low-contrast images, but we find it quite useful for hiding sensitive data. Some examples:
I think it's kinda hard to see on the wikipedia example what has been redacted. I just do "Obfuscate" in Greenshot with pixel size 16. Call me when this algorithm reverses this https://i.imgur.com/NYf0Dpe.png! :D
