OK, tried it on an iPhone SE 3rd generation (least powerful of new phones) and it works on 500 or so at a time. Quits at some unknown point between that and 4500.

Observations: the groups are somewhat redundant. I take a lot of snaps of Yosemite webams and WQXR screens in the middle of the night so I can remember the unusual piece I woke up and heard [0]. There are several groups of webcam photos, and in the group, none identical. Clouds make unique and similar (fascinating) patterns, especially when half dome's peak is above them.

I really don't care about duplicates. I can start clean any day, and some duplicates are just an annotated photo (meme) with the original lying around in case I get a better idea.

Here's the deal. Now and then, I copy the entire roll to the computer, so I could empty the phone any old day, but if I could capture those groups, the large ones, and perhaps tag or rename the photos, it would help me enormously to avoid the endless search for that ONE graphic I want to post RIGHT NOW. Apple image search is a terribly bad joke.

So this is the first free (almost) image characterization app I've seen, a hopeful sign.

Some days, I am tempted to rename every one of 6000 photos on the computer just so I can find the one I want.

Groups would help.

Thanks!

[0] In the boondocks, I like some music to mask weird sounds. One night, it was a group of foxes. I was using an iPad Air 2 to do this but it sprouted a bulge indicating possible battery explosion, so it is getting wiped and recycled. I took snaps on the phone, which was next to me (in silent mode).

Experiment stopped.