When I edit a photo in Preview, its thumbnail icon changes to a generic jpg icon. That's annoying in itself. Took me forever to find the trick online -- also annoying that it's not straightforward, that you have to be privy to some secret knowledge to know what to do. Anyway, so I found that the way to remedy it is to go to info, click on the icon in the upper left corner, and delete it to get the photo's icon to show up in Finder. Yay, except it's an image of the photo before it was edited. This is a problem particularly when I've changed the photo's orientation.

I'm sort of perplexed as to why this is even an issue. The only help I've found in my searches online says just to download a graphics converter that does thumbnails. Really? This seems like such a basic file organization thing, it's hard for me to believe that Apple didn't program it in.