I currently use hypothesis as a way to take notes on web pages and save ideas for future reflection. I'd like to be able to save images or diagrams as well. Polar (https://getpolarized.io/
) currently has a basic interface for doing this that could be used as a model.
Because I cannot add images here, I've attached a pdf that explains how this is currently implemented. While I do not think this is a particularly streamlined implementation, you can get a sense of the functionality.