I have experience with using small rigid bodies on fingers.
What cameras are you working with and how many cameras do you have. I can suggest camera placement as well.
Please have a look at our online store where can order 3 or 4mm hemisphere markers. : http://www.naturalpoint.com/optitrack/p ... s-markers/
You can do something simple like stick a band-aid around your finger and place the markers on the top of the knuckles. I have seen some people use hard pieces of plastic and double-sided tape to stick to the skin, then place the markers on top of the plastic. Or you could use a glove that velcro can stick to, and have the pieces of plastic have velcro as well. Then you could adjust the placement of the plastic rigid objects on individual users of the glove.
You will need to use at least 3 markers to make a rigid segment, and I suggest using four or five markers. Place the markers in a way that they are in an asymmetric pattern and have the markers spaced out about two marker widths away from each other. There needs to be a decent amount of separation between the markers and the cameras will probably need to be fine-tuned for focusing. Depending on the distance from the camera and the resolution of the camera, markers that small and that close together may seem to blend in together in the 2D view and may not be able to be seen as individual markers. At that point, you will want to bring the cameras closer or check focus.
As an example, please watch this video from our customer, Oblong. http://oblong.com/what-we-do/g-speak
On this page you will see a person who has their hand extended, wearing a glove with rigid segments as I described above.
Please let us know if you have any other questions.
Technical Sales Engineer