E-mail 'xface'-feature incompatibility ?

Hi, I discussed recently with few list-members, that the xface pictures I receive in companion to their e-mails is not always identical with the originals they wanted to 'distribute'. Seemingly there is an incompatibility between the different e-mail cliens, e.g. I use Sylpheed-Claws and in case I get an e-mail tagged by Kmail, always the same thumbnail arrives to my side, but seemingly it has _nothing_ to do with the one sent out with that particular e-mail! Is this xface-feature something like the picture-messaging (via SMS) of older mobile-phones, which was nice, but could be correctly interpreted exclusively by the product of the same company?! Thanks, Pelibali