You are correct that it's not possible to create a fully 3-dimensional organic object in the round from a 2D image. The best she'll be able to do is a low relief, using a heightfield algorithm.

It always amazes me that people spend a lot of money on 3D printers but refuse to pay a penny for the software that would enable them to use them to create parts of their choice. Yes, there are free programs out there, but no, they won't necessarily do what you need, especially not easily.

For the young lady who wants to build a Pokemon (TM) figure, I'd suggest Cubify Sculpt http://cubify.com/products/sculpt . It's a Windows program, so your Macs would need to be able to run Windows to use it, but it uses a very intuitive "virtual clay" interface that shouldn't be hard for your students to master. The free demo will work for a couple of weeks, after which it's $129. It works best with the 3D force-feedback stylus, but it works okay with a mouse. It outputs STL files that should print without issues, especially if you run them through a program like Netfabb or Meshmixer to provide supports.

If you need help with any of this, send me a message or give me a call (not too early in the morning...)

Andrew Werby
www.computersculpture.com