So The Flowers of Robert Mapplethorpe is often a bit of a punchline as a CD-i disc, but it's also a really interesting demonstration of the difference between CD-i and Photo CD and how each could represent its own strengths.
Photo CD is technically what's known as a "CD-i Bridge" format, which basically just means that every Photo CD has a CD-i program on the disc and implements a subset of the format. That usually doesn't mean very much: a Photo CD typically runs the same on a CD-i or anything else. But it's possible for a Photo CD disc to have a CD-i program that actually has a different, CD-i specific presentation of the content, and a few early discs did!
The Flowers of Robert Mapplethorpe is a good example. It's marketed as both a Photo CD disc and a CD-i disc, and it really is both. It doesn't look identical between the two formats at all; instead, it runs differently depending on what you're running it on, with distinct presentations playing to each platform's strengths.
On the Photo CD side, it's limited to still images and audio. Photo CD doesn't support animated transitions between images, so you get hard cuts anytime the content changes. On the CD-i side, on the other hand, you get animated transitions between screens that lends the whole thing an extra sense of polish and professionalism. The CD-i wasn't designed to do higher-resolution images, however, so it runs at half the resolution and has far less detail as a result.
Here's screenshots demonstrating the difference - left is Photo CD, right is CD-i (with some emulation glitches from MAME).