Steganography

what is the decryption scheme using the key?

May be it is too late for you aminos101 (I see you have validated this challenge long time ago).
For those who need it, the full file name has a small hint on how to decrypt the pass :)

xchess64, are you talking about the ppm extension? Because the full filename is ch8.ppm so I am not sure if you are talking about that filename

Sure, that’s the hint