Locked image files?

[twang]

Hi.

I'm trying to modify the playing cards on Titan Poker (i-poker network, Playtech software) but the image files won't open. I get error messages that says something like "couldn't parse the file" and "couldn't read file header". I've tried open the files in Photoshop, Gimp and Irfanview. Any ideas how to work around this?