If images are royalty free or your own there shouldnt be a problem. There just needs to be a link to something indicating the image is copyright or royalty free, which it looks like you have done. I wouldnt worry about to too much. The only thing I'd suggest is putting "photo by author" under pictures you took.

As for reading/commenting lots, it's really unclear what the threshold is where they consider it spam. I do know Medium tracks reader's scrolling on stories and that's taken into account when they look at "genuine" engagement. If you're reading normally before commenting, there shouldn't be anything to worry about.