Create an image repository
I haven't tried something like this before, but one way to solve it would be to.


Create a node type to hold the images.
Create a node reference to the image node type.


This would allow you to have several nodes reference the same image node type. You would also be able to tag images and use views on them, if you wanted to display the images stand alone, in a gallery etc.

You would need to do some work, to theme the images the are referenced though the image node, but it shouldn't be a big deal.