Measuring bitmap image sftwre

[rodan]

Anyone ever use any software used to measure a circumference item on a bitmap image? I've been scouring the net, shareware and software sites. What I'm after is something that can measure as accurate as a cad, drafting software, but, quick and easy to use, and, of course, accurate. The item to measure are "centers" on shooting match boards, scanned into Windows bitmap, and, would like it magnified, and, high pixel. If anyone has any ideas, please post.