I've always thought this was possible. Now with this piece of software, you can measure anything just by taking a picture of it. If you ask me, that is awesome! It is not free (I wish) so I haven't tried it but the guys guarantee a very accurate measure as accurate as 1/32 of an inch. This is way cool... now if I can just find a free trial.
iPhotoMEASURE - The Contractors Photo Measuring Tool