Forum Moderators: open
I have seen problems with images in OS X 10.1 & 10.2 but I have not nailed down a way to fix them other than to upgrade to 10.3, the problems range from skewed images that are resized using html, images that do not display (sometimes or never) and it is usually a problem with the HTML pointing to the file.
Check the source of the e-mail that is received by the Mac and see if the problem is there.
(One option I'm considering is to create a PDF to send rather than the html formatted e-mail.)