Deleting ipod photos from my macbook

I have quite a number of pictures in my macbook and was wondering where all my space was going. I think itunes is creating smaller versions of my pictures so that they fit the format of the ipod and it is taking up lots of space on my computer. Where can I find these pictures on my computer so I can delete them? I don't want to delete the originals, just the ones that itunes generates. Any help would be much appreciated! Thanks!