The Se's are free loaders taking you for a ride - a free one, I might add, at your expense.
Bing is worse than Google, sending visitors to your image url with no possibility of browsing through your site.
It really is time for webmasters to be highly selective about what they give to the engines.
I've banned Google and Bing from indexing my image folders a few weeks ago, and went further with Bing requesting they remove all my images from their index.
I am now watching my bottom line intently to see if it has had any effect whatsover. So far none, but it is eary days.
I don't have time at the moment, to see if there is a way to exploit image search for my site's benefit, but I suggest you read lucys thread about the topic, here: [webmasterworld.com...]
I'm curious too, if throttling is taking place, whether those image hits count towards your cap? Because I know what traffic I would prefer, but I would bow to other people's expertise here whether in fact this is or could be the case.