When I need to create an image loop prior to a presentation, I'll
usually create a custom looping show for the first number of slides
with an invisible action button that lets me click and exit into the
main presentation whose slides follow.

But...the slide to slide transitions are not as slow and elegant as
internal image fade entrances. So, is there a way to have a true
looping series of full screen images on a single slide? I know that I
could keep repeating appearing and disappearing animations of
overlapping images, but that's technically not a loop and will run out
at some point. Is there a way with "repeat animation" or something like
that to do this?