Photography helped the identification of birds a lot. When two species are very similar it often used to be impossible to identify them in the field, especially when not given very good views. With digital photography this all changed. Where birders only had brief glimpses of certain birds, they now could take a picture and could have a good look at home at what they had seen. And when the equipment improved and became more affordable (or people were willing to spent more money…) the pictures improved as well and even more was possible.
This picture shows two species of prion, the Antarctic Prion on the left and the Slender-billed Prion on the right. Differences are tiny, the left bird has a little bit more black on the tail, is a little darker and has a little different facial pattern. All things that are very difficult to see when the birds are flying next to the boat, but on a picture like this are clearly visible.