For the record, markwmsn asked if you were seeing these pictures using the Photos app, or if you were looking in Finder folders. He did not ask you to look inside the Photos Library package. I thought it was important to warn you before you did some damage. Hence the all caps!
So, apparently you are looking at pictures using the Photos app. In Photos, we can store pictures in multiple albums, so the picture of "Aunt Ethel at the Grand Canyon" can be in the "Aunt Ethel" album with other pictures of Aunt Ethel, and it can also be in the "Grand Canyon" album with pictures of other people at the Grand Canyon. And it can also be in a the "September 2015" album with other things that happened then.
Keep in mind that, in Photos, pictures aren't exactly "in" an album. When you "put a picture into an album," its name is added to a list of pictures from the Library that display together when the album is clicked, kind of like a music playlist, but for pictures. It takes no extra storage space to have a picture in several albums. As you can imagine, this is very powerful in organizing pictures.
In Sequoia (which I understand you can't use,) for the first time Photos can show all the albums that a picture is in. But that is not available in Ventura. Before Sequoia, we used the trusted 3rd party app PowerPhotos ($30) to tell all the albums that referenced a picture file, as well as for lots of other stuff.
Ventura was the first OS that showed us actual duplicate files. In the Duplicates section, you may find two different copies of a picture in two different albums. Photos will "merge" the two, meaning it will delete one of the two and include the remaining picture in all the albums that either was in.
Does that help?