How to find an image within another image using python

I'm trying to use python to determine if one (small) image is within another (large) image.

Any suggestions before I take myself completely down the wrong path?

/edit: Ok, some ideas: I'm using PIL, and I'm converting each image to the 'P' mode so I can compare each pixel as an integer. I'm trying to implement something like a Boyer–Moore string search or the Knuth–Morris–Pratt algorithm, but in 2 dimensions.

Maybe this will help: instead of searching for ABC in XXXABCXXX (answer=4) we are searching for

ABC    
DEF    
GHI    

in

XXXXX        
XABCX        
XDEFX       
XGHIX    
XXXXX  

(answer=(2,2))