Thomas and I have created a plugin for JOSM called AreaSelector, which allows you to create objects from background imagery. It was build to help mapping buildings based on imagery from basemap.at, but it could also be used for other imagery.
The plugin creates an image from all background layer and creates a polygon around the point you clicked. The analysis is based on the color at the click point. It may not create the perfect shape, but I think it’s a good base for mapping buildings.
A building tag dialog will automatically appear with the last values remembered. That makes it easier if you map multiple buildings in one street, so you don’t have to enter street, city aso. every time.
I would be happy to get some feedback what you think about the plugin!
slightly a different topic (since you’re into image processing)
Can you make a plugin to zoom mapbox images (which has max zoom = 17) to interpolate to higher resolutions in a much prettier way like in ID editor? Currently, those mapbox images look very blocky in JOSM when interpolated at higher zoom range.