The software people are inventing just keeps getting more and more impressive. Unlike other picture to model software, which leaves questionable results, the makers of 3D-Sweep really seem to be onto something.
To use the software, simply outline the shape you want to define on a 2D plane and sweep that shape along the third plane. The software recognizes depth perception and even follows the curve in the object along the path.
But why do you need me to explain it, when you could just watch the video?