This has always looked like a neat idea but after seeing the article in the latest Digital machinist I decided to make one this weekend. I picked up a cheap logitech webcam for under 30$ and dug out some scrap hunks of aluminum. Made a new housing with setscrew adjusters to dial it into the spindle centerline.
Well it works pretty darn good. It can be used for measuring, inspection and edge and corner finding,punch mark location and bore location.
If the surface edge is sharp I found it reliable to under .0005" finding both edges of a square corner. Within a .001" on a bore. The sharper the surface edge the more accurate it is. Bevels on the edges make it more difficult but you can still get very close. Probably can find a lot of uses for it. Punch marks look like craters.