I work in the forensics field and often taken close up pictures that contain a ruler or/scale. It is very important that the photos are printed so that the scale/ruler is exactly the same size. For instance, a fingerprint photographed with a scale that indicates it is one inch long, when printed needs to be exactly one inch long. In the darkroom, I would just use a scale that is exactly like the one in the photo, and adjust the enlarger head until they line up exactly. When the image prints, the scale is perfect. Is there any way to accomplish this using Photoshop. So far the only way I have been able to accomplish this is to print out a bunch of different pictures changing the image size until finally I am able to match the
rulers. Any help would be so appreciated.
I just ran across a utilty program called Caliper from Iconico that's designed to measure screen elements in a variety of increments including inches. It works by calibrating the tool with a known measurement and then basing subsequent measurements on the calibration. I have not used this tool extensively, just a quick go-around with the demo, however it has received high marks from the NAPP and from what I can tell, should suit your purposes. Check out the demo and let me know how it works.
They have a Compass and a Protractor tool too.