SiteCatalyst is a great tracking choice as Sham suggested, but I'm still a bit curious about your question.
Do you want to track how many times an image has been showed for visitors or how often an image has been rendered from the DAM ?
It sounds like you are aiming for an approach of adding a variable (in the form of metadata) that is incremented every time an image is fetched from the DAM. Since one hopefully will use the wonderful world of caching, most of the time an image would rather be served from the cache/dispatcher instead of being rendered from the DAM on the publish instance or the dispatcher (provided that the cache has been set up properly). I would say that this approach would be quite inconvenient and possibly slow things down. On top of it all it might not work at all except on the author instance
If you instead have a link to lets say a full-scale image from a thumbnail it could be really easy to track clicks on that link with e.g. SiteCatalyst. The problem as I see it would be if you need to count those things without any links. If you have only one picture on each page however, SiteCatalyst would without any problem be able to track the page views and thereby also the image views. But in the case where there is more than one image on each page or when an image can be on several pages it could become quite messy. As far as I know, I don't think SiteCatalyst can track just displayed images on a page (corrections anyone ?)
Then you will probably have to write you own javascript code that will fire an event every time a page has loaded and for each of the images on it. After that you will have to record that data somewhere and then later on transfer it back into the author that could update the publishers. That could be a bit tedious as you probably figured out. But it's always good to look around and see what other options there are, I've seen that some people really like to combine the efforts of SiteCatalysts and e.g Google Analytics and maybe this can be something for you.
Good Luck :)
/Johan
