I have an initial set of test images to work with now. Sadly, the information I wanted in the file names is not what got put there (the original code was placed after the relevant variable had been re-used for something less useful and I failed to notice that when adapting it). It's not a big deal because I can just replicate the code and have it load data from a file instead of from a camera, but it's more work to get started on the analysis than I hoped.