>>1825520 (LB)
>>1825832 (LB)
>>1825875 (LB)
Update in discussion in last bread:
I finished digging around in the bikerack pic with a hex editor. I pulled out the raw IDAT chunks, stitched them together, and ran them through zlib-flate -uncompress. The output was the correct length (close enough, some extra null bytes).
There is no additional hidden info in the file structure. These files are huge simply because they're high-rez, high bit-depth, and because PNGs suck for photos.