Do you mean iPhoto or Photos? iPhotos hasn't been supported for years. I'll tell you about Photos, and I think I remember that it was similar in iPhoto
Albums don't have pictures in them-- they have lists of pictures from the Library. That way Aunt Bertha at the Grand Canyon can be both in the album labeled "Aunt Bertha" and in the album labeled "Grand Canyon." Hitting Delete removes that picture from the list, but doesn't change the picture.
The Library view shows all the pictures in the Library. You can select all of those and use command-delete to delete them all-- they'll be removed from all the albums, their names can't be there any more.
EXCEPT-- there's a special album called Recently Deleted. All the pictures you deleted are still in there! They go away permanently in 30 days. But, you can select them all and delete them and be rid of them forever.
Alternatively, you can find the Photos Library, drag it to the trash, and empty the trash.