Ask HN: Machine Vision Problem?

This is actually for a good cause (a small food bank). I talk to a gleaner at the Safeway almost every week. He has a problem that someone must have solved already, at least in pieces, and it's way too hard for their resources: They have a need to weigh their food, but weighing each individual item is much too much trouble. So they'd like to estimate it from a photo. For example, if they filled up a palette with all drinks, it'd be 1,600 pounds, which is too much, but bread is much lighter. You get the idea. So it's basically a machine vision problem for packages, where the packages can be grouped into one of a small number of categories. They can give a weight range for each category. This is not an organization with money to spend, so it needs to be a free app, which I can probably customize for them if it's not too much work.