Open source Software to find and extract scanned negative frames from Kodak Disc and Minox negatives

I am looking for open source software that will find negatives on a sheet of scanned negatives and extract each one. Some of these negatives are Kodak disc, so the software needs to find rectangles of arbitrary rotation, rotate the images, and create new files. All of the rectangles are the same size.

This sounds like a capstone project in a computer science image processing course. It can’t be that hard to do, and it seems like a common request, but I haven’t found anything. If I can’t find the software, what are the building blocks that I would use to write it myself?

EDIT:

I found this blog post which provides a ksh script that uses trigonometry to compute the location of the disc images from three control points. This is super-cool, but you need to manually find the control points. And it doesn’t work with my other negatives, which are from a minox camera.

(For those who are interested, I am scanning the Minox images by laying them flat on my Epson flatbed scanner and covering them with a block of optical glass, and then using the scanner’s transparency mode.)