Hand Size Estimation

I'm trying to estimate the area of hand. It does not need to be accurate; just a estimation is enough.
I'm thinking of using ultrasonic sensors to sweep along the width of hand and estimate the area of hand proportionally.
However, sensors that could measure the width costs too much for a class project.
How should I go on with this idea?
Does anyone have any other ideas that might make it more easier?

Scan the hand with a cheap USB flatbed scanner. Set it to a low resolution to improve speed. Then calc area based on the bitmap.

Is there a software or like a code I could look into so that I would be able to calculate the area based on the bitmap?

Can't you jsut threshold each pixel and count how many pass the threshold? Perhaps use a fudge factor to help get things a bit more accurate if not all areas of the hand are scanned.

That should work. If you put a black paper over the hand eveything that is not hand should scan very dark, so you can set the threshold quite low and just count pixels.

As a faster method, why not use a webcam pointing down, with the hand on a black paper card? It should be pretty accurate if the hand is flat on a surface and distances remain constant.