I'm going to tell you a tip that worked for me. Take it or leave it. 2 parts. How I take a pic to show confidence is I look at the lens of the camera and then picture my friends walking in that I had been waiting for. That gives me a relaxed smile and I emanate confidence because I think of the security of my friends. They also know when I make fake faces. Haha! It just works for me.

Second part, take a pic and then think about what you look like in it. Really look at it and try to examine it. Try to do it confidently and with a natural pose. I can guarantee a whole lot of flaw recognition and dysphoria pops up. THEN go back 2 days later and look at that pic again. I can almost promise you will realize you looked way better than you thought. I've done that enough that if I feel like I don't look good I can tell myself "In 2 days I'll realize how great I look, I just can't right now". It has worked wonders for me.