The 20x26 example is indeed scary, but in line with what was known about facial recognition. (It also becomes a bit less scary when you don't look at a zoomed-in version of the image.)
Hence my suggestion to reduce a face to something like 5x5 blocks.
While I'm familiar with the crypto design problem, this is not a crypto algorithm. Sure, it can't be ruled out that someone in the future will find a way to do it, but the state of the art says that 5x5 pixels are not anywhere near enough to run face recognition.
And a solution that may be broken in the future is often much better than a solution that people don't use because it doesn't meet their needs, which in this case is not having fugly black boxes in their picture.
Hence my suggestion to reduce a face to something like 5x5 blocks.
While I'm familiar with the crypto design problem, this is not a crypto algorithm. Sure, it can't be ruled out that someone in the future will find a way to do it, but the state of the art says that 5x5 pixels are not anywhere near enough to run face recognition.
And a solution that may be broken in the future is often much better than a solution that people don't use because it doesn't meet their needs, which in this case is not having fugly black boxes in their picture.