George is using Google Photos. But he's getting a lot of duplications as he backs up from his desktop, phone and laptop. Leo says that's a common problem, but is usually due to different formats, like RAW and JPG. There's no real way to automatically weed the duplicates out. Picasa used to have that option, but Google killed it and didn't port that feature over to Photos. Leo suggests backing photos from a camera to the phone and let Google Photos upload from that one source. He can also use the sort feature to search for day-of capture and then manually de-dupe from there.
George can also delete everything and start over, but that's an extreme solution. Many photographers just live with duplications.
From the chatroom - https://www.wikihow.com/Delete-Duplicates-on-Google-Photos