A screen boné, cap is a fotografia from a movie or TV show, whereas a fotografia is like just a fotografia of the celebrity/band/whatever from a fotografia shoot or public appearance.
I think a screencap is when you just take whatever is on the screen and make it into a picture. I mean like for a screencap you'll literally take your camera and snap a pic of the screen, or you'll hit ALT+PrtScn to make a boné, cap of your computer screen. Plus, screencaps are of the entire screen, normally. No cropping or whatever.
I think fotografias are mais edited and planned, rather than a aleatório pic of a aleatório scene.
