Automatically Crop large batch of photo scans

I have 3,200 images in jpeg format that are scans taken with a background that is black with white markings on it. Ideally I need someone who knows how to automate the process of cropping out the background. Most of the images are aligned correctly but some will require slight rotation prior to cropping. And also some scans contain multiple images, each of which would need to be cropped. I need this done with no downsampling (except the inevitable resampling which occurs with rotation). Very small amounts of rotation do not need to be corrected (we can discuss the threshold). I am attaching examples. I am paying $100 flat fee. Obviously that makes it suited to someone who knows how to automate this process, as it would take a lot more time/effort for this to be done manually.