This isn't a native capability of FileMaker, but I seem to recall that there is a plug in that offers this type of thing. You might search for FileMaker Plug Ins and see what is available.
Depending on the degree of detail needed, you might also be able to set up a grid of transparent container fields that overlays the human body image. The fields could be set up as buttons such that clicking one fills that field with a partially opaque color to "highlight" that location of the body underneath. This can be set up so that clicking the button a second time clears the highlight.