> why not use three cameras simultaneously, each from a different angle, then classify the three images? Those cameras must be nearly free in cost.

Because you really only need one camera (and two mirrors).

> Also, to get more training data, what about setting up a puffer to blow the part back on the belt and tumble it?

That's an interesting and novel idea. It probably will not work because the difference between the heaviest and the lightest parts are such that you'd blow most of the parts clear off the belt. Also the camera is sampling fast enough that the part would end up imaged in many positions without the ability to stitch the parts together again. But interesting.

> And question: do you normalize out color at any stage? As in, classify a black and white image, with a separate classifier for the color?

No, but I am considering using HSV or LAB as the colorspace to see if that improves accuracy or reduces training time to get to a given accuracy.