How do I overlay pictures in iMovie?

Completely ridiculous to have to do that, given how simple it is on the computer version!! Why do the iPad versions of iMovie and GarageBand have to be so frustratingly limited? But thank-you very much for your solution to the problem.

You can't overlay photos (at least not directly).

If you still want to do it, create a separate movie project in iMovie and include only the photos you'd like to overlay in your original project (essentially make a slideshow, and be sure to either disable Ken Burns or set it appropriately for each photo). When you're satisfied, export that movie to the camera roll. Now back in your original project, open the media browser, locate the slideshow your created and tap on it. Tap the three dots (...) and choose the type of overlay you want (cut-away, pip, or side by side).