1. I have 3 pictures of Jo.
2. I have 3 photos of Jo.
What are the difference between pictures and photos?
Not a lot, they are often used interchangeably in BrE (at least I do).
Having said that, there are some subtle differences:
Pictures - could refer to drawings, paintings or other art forms. Created by pencil, crayon, paint etc.
Photos - Refers to photographs only. Created by a camera.