iLucian

Re-reading my post, it doesn't look at all clear so will try again :S

If the problem is how do you identify the part of the finger you want to measure then a possible solution is to follow the motion capture technique of attaching something easy to identify to the part you are interested in. Poser can do something similar, it is very common for users to attach an object such as a ring to a character's finger. When the finger (or any part of the character) is moved Poser ensures the ring follows the finger. In the Poser user interface this is achieved by selecting an object and via it's property form and setting it's parent to the part you want to follow.

If the depth-map script doesn't allow you to select the part to measure, maybe combing this approach with the script will.  

Good luck