I didn't know how to change my pic, than I found out how, then I figured out how to use a GIF! In Scratch you have to write code for a project GIF to work. Like: When green flag clicked, forever, wait 0.02 seconds, then next costume.
For Profile pics, scratch automatically makes them work. Just for the stupid people like me who cant figure this out (FIY everyone's smart in their on way!)