SidDev, I do not know if I completely understand what you are saying.
You say that you wish to create an avatar from the point cloud of a single object?
When you export a point cloud from Photosynth, you can open it in a 3D model editor such as Meshlab and delete any points which are not part of the object you wish to model. This would be one way of cleaning the point cloud to only the points of the object you care about.
Another way of going about getting a point cloud of a single object would be to edit the photos before you synth them in a photo editor, painting out all parts of the photo that you do not wish to see in the point cloud. I would use black to paint out unwanted details, but any solid color should do. Also note that I do not recommend doing this without first making a backup of the original photos.
Am I answering your question or not?