Many thanks for all the kind comments. To answer Alex and Jonathan's point - Yes it is pretty hard to click the photobomb images. That's because I am useless at all video games and I wanted to get my own back on all those millennials and other young guys who are adept at this sort of thing, by making a 'game' that I can actually win! Once you run through it a couple of times you can locate the position of the hotspots and complete it fairly easily.
Second - Ed's question - How did I get the character to appear behind the foreground footage - and thanks for noticing Ed!
This was achieved in After Effects. Using the Rotobrush tool, you draw around an object in the footage that you want to cut out - e.g. in this movie one of the objects was the helmet rolling on the ground. You then check frame by frame that the object is being accurately tracked and make any necessary adjustments - then you render it by clicking a 'freeze' button in AE. To maximise the chances of good tracking, it is recommended to select objects that stand out in clear contrast from the back ground. The rendered footage will be of the object you have selected. You then copy the original footage to the base layer, place the character (in my case the robot head) on the second layer and on the top layer we have the footage of the extracted object. That's more-or-less it.