Overlaying still photos/slides in video for iMovie 2.2.1
As the title suggests, I'm having trouble overlaying still photos/slides into my iMovie (2.2.1) video for my iPad Mini. Overlaying videos into other videos is easy, but overlaying photos seem to be more problematic for some reason. If it's simply not possible, I was further wondering if it would be possible to video record still photos/slides and overlay them that way. I have searched around, but have no idea how to do this. Any suggestions would be hugely appreciated. Thanks.
iPad Mini, iOS 9.2