I found a software that someone finally implimented, it involves using a credit card/similar size object, and it has a box object that it imposes over the picture taken, and compares relative to that box (can be shrunk or enlarged using the touch wheel) then a vector line is created to calculate the approximate length.
The only problem is that it needs to be taken at a parallel angle otherwise it doesn't work too well on angled objects.
It requires .Net compact framework 3.5:
It is called
DarkRuler. <- *link*
screenshot of it in action, its still not super accurate but does the job
