For System 7 through OS 9.2.2, I recommend JPEGView. For OS X, I recommend Phoenix Slides.

If the images are JPEGs, JPEGView can be set up to start a slideshow when launched, and it will repeat the slideshow indefinitely.

I set up a digital picture frame with a 5300 (and a Wallstreet, but I never finished the write-up) that I describe here: 5300 Digital Picture Frame It uses JPEGView to drive the slideshow.

Enjoy,
Drew
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Power to the PowerPC!