Adding a scale

It would be useful to be able to add a small scale/ruler and size it, reposition it, change font, and change background color. With a macro image there is often not a good point of size reference in the image. It could have fixed or vairable nomenclature (mm, cm, in.). If you wanted to get really creative you could add the capability to substitute a small picture for reference (e.g. pencil lead, pinhead, penny, human hair) that would be placed into the layer instead of a ruler and could have the size of the image adjusted.