I believe that the mismatch is because I had my local copies of png images recompressed (with pngout) with a higher optimization setting than the default used in the above. Since pngs are lossless, this only makes the file size smaller, but doesn't cause any loss of detail. Still, that's more than enough to make a checksum missmatch. Sorry about that, I must've forgotten about it, when I uploaded the image. However, that was the original source.