An easy solution is to put the link in the description and have it show.  You enter the description when you add an item so you could add the link there along with any text you wanted.  Not as elegant as adding it to the image, but it would work.

On a side note, the example you mentioned above is exactly how the announcement module works.  You enter announcements and pick links for the read more (a page or a url).  But you don't get the nice searching capabilities that you have in the Repository module.