How do I create a spot the difference ungraded question?

This is something I developed a while ago using a Pick Many Freeform Question, where hotspots served as targets. Hidden oval shapes were designed to change to their normal state when the corresponding hotspots were clicked, visually indicating a correct selection on the original photo and removing the hotspots on the photo with differences. While it was initially intended to be a timed game rather than a question to be submitted, it could easily be adapted for submission based on the number of correct clicks. If you're interested in exploring this further, I can upload the .story file to demonstrate how this was achieved. You can preview this interaction here