You want it visually identical but not necessarily bit-for-bit identical. Compression and transcoding should not cause validation to fail unless the compression artifacts are particularly severe, but even a tiny, one-pixel change that substantially alters the appearance of the photo should cause validation to fail.
And yes I agree this is hard to quantify and impossible with existing algorithms, that was my point.
You want it visually identical but not necessarily bit-for-bit identical. Compression and transcoding should not cause validation to fail unless the compression artifacts are particularly severe, but even a tiny, one-pixel change that substantially alters the appearance of the photo should cause validation to fail.
And yes I agree this is hard to quantify and impossible with existing algorithms, that was my point.