I have about 25 images that I would like to show on the green screen in the background. I've been playing around a bit more with Studio, and that's what I was missing.
I can either use the Image Overlay element and stack 25 boxes with my PIP Webcam as the top box. The easier option is Slide Show with PIP Webcam together in one box, and then just click through the Slide Show images. I have to remember to click on pause in the Slide Show so that the image only changes when I click them explicitly. I suppose this was the gist of my previous post was to allow the option to turn on/off Auto Play on the Slide Show just as it is in the Movie video source.
The nice thing with the Image Overlay element, though, it has scaling, positioning, etc, whereas the Slide Show is pretty much just a slide show as advertised. I have to make sure the resolution of the images matches my selected camera, otherwise there will be borders around the image.
It's more of a learning / work flow issue on my part than anything else.