As an ex-professional photographer I know it's possible to take a 6 and turn them into a 10 simply by having them stand up straight.
If you want to know what perfect posture is then find a blank wall, stand with your back to the wall. Your heels, bum, shoulder blades and head should all touch the wall. Now pull your shoulders back so that they are inline with your ears. This was taught to me by a physiotherapist friend while I was recovering from a ruptured disk in my back. I know it will feel weird at first but it will become your natural posture over time.
Proper posture will flatten the tummy somewhat and make the chest appear bigger.