# man pages on Debian Linux
pgm - man pgm
pbm - man pbm
ppm - man ppm
pam - man pam (portable arbitrary map)
png - http://www.w3.org/TR/PNG/
gif - zless /usr/share/doc/libungif4g/gif89.txt.gz
bmp - fileformatdocs/bmp.txt (and MSDN)
ico - http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnwui/html/msdn_icons.asp

TGA

http://paulbourke.net/dataformats/tga/