I'm answering your private message here because maybe other people would like to know how I make the "Find the differences" exercises. It's not a secret! In fact, I've added the information to the bottom of the relevant exercise so other teachers don't have to wonder how they were made.
You mention making "hot spots" on images and doing "a 'find the differences' with a picture, and the listeners have to click on the image wherever it is different from the recording. That sounds like a great idea! Except that I don't know how to make hot spots on images in Hot Potatoes. Now it's your turn to explain.