I have a Macbook Pro laptop and an iMac desktop. The software is Apple's Photos.
When I got back from our trip, I was pleased to see photographs already in the desktop, but then I noticed that whatever was happening, it stopped midway through the trip. Hundreds of photos traveled from one computer to the other without my doing anything. Then whatever was happening stopped.
UPDATE: I figured out the problem. It's "Photo Stream." Photos automatically became available to all my computers but the memory maxed out. I found the photos under the tab "Albums" in Photos, and I was going to delete them so that newer photos would move from the laptop to the desktop, but it said that deleting them in Photo Stream would delete them in all my computers! That might be good for some people, but it's not what I want.