get x,y mouse coords in an image

Using Yosemite (10.10.1), how can I get the x,y coordinates of the cursor in an image? For example, in Preview if I move the cursor to the corner of a rectangle, and I can see that, relative to the image, it is located at 200,200. Except that, I don't see how to do that in Preview. I can approximate it by drawing a rectangle starting at 0,0, since Preview will tell me the lower right corner of the selection.

If it's not possible to do this in Preview, can you either recommend another app, or recommend a way to find out? (Hate to buy something hoping a feature is there, then find out it is not.)