I have a url to an image and I am trying to search for all pages that have it in their sources. Is it possible?
Until, or unless, something like Opera's MAMA (Metadata Analysis and Mining Application) goes public and allows for the searching of HTML source code of public sites, you're out of luck.
Currently, there are no search engines that provide this feature.
Best way to find out if a site is using one of your images directly in their source is to check out your site logs.
Paying attention to the images, look to see who the referring website is and then go to that page and view the HTML source code the old fashioned way. This is not reliable as the referrer can often be blanked out, but it's what you can do for now.