lucy24 - 8:12 am on Jul 21, 2013 (gmt 0)
Google image bot passes your domain as referrer when loading images
Er, no it doesn't. Search engines request images "cold", without referer. Look at your logs.
since Google.com cannot display said image they display their own lower resolution cache copy instead
They do this anyway. When a human clicks on an item in Image Search, google immediately requests the image from your site-- but it isn't actually displayed until the searcher proceeds to the next step, "display the image". Meanwhile they see the cached version. The effect is to make the search engine-- and your own site!-- look good because the image is ready and waiting in user's browser cache, and comes up with no delay.
Bing links their images directly to your image url and not the page url the image is on
So does the new google image search. It was unrolled, oh, at least a year ago. Are you returning after a long absence? Or using an older browser? (Not necessarily de facto old. Just "old" according to google's UA detection.)