comparing 2 images

[Joe Green]

Hello,

I would like to take 2 images (scanned) and compare them to see if
they are similar. An example (but not limited to), would be 2
signatures.

What would be the most suitable library/module to use for this (if
any). I have been looking through the PIL documentation (yet to look
into ImageMagick). Am I knocking down the wrong doors? Is this even
do-able in Python (I need to maintain portability)?

Any hints/guides/references would also be greatly appreciated.

Thank you.