That's the general idea of it. As long as all the images are taken from close to the same angle - the heights should be pretty close. Still not as good as actually measuring figures - but even that isn't fool proof.
Right now I have 60 miniatures in there, and I will hopefully have 60 more by the end of the night. If I can manage to maintain that rate till I leave for a trip on Friday...it should be pretty comprehensive - or at least remotely useful.
Also, if anyone notices problems with it (either in execution or inaccuracies) let me know.