I've started collecting some smaller metal tokens and am looking for a way to measure them and show their measurements in the scans I make.

I was thinking of scanning a gridwork marked with millimeter measurements to use as a reference, then cropping each token scan and overlaying it on top of the grid. But, If I could simply add a layer to each scan that was transparent except for a metric ruler along the top or side or both it would be much easier and look better.

Has anybody else done this sort of thing? I don't want to try to re-invent the wheel if it's already been done. This seems like the kind of thing that would be readily available somewhere online (knowing that anything found online might have to be re-sized to correspond with the size of the item I am scanning).