If you can't see photo credit on your post pages here's how you can enable it :
1.Go to the layout and design tool from the left menu.
2.Go to post page options from here :
3.Select the load media element here :
and go to the options on your right here :
4.Scroll through them until you find photo credit option :
5.Move the element in the order you want it on your post page and chose it's layout to enable it and make sure it's not hidden.
6.Save the changes.
Photo credits should be showing on post pages.