Karyne Levy/Business Insider
Once you're in the camera app, you can either take a picture using the round button on the screen, or you can take a picture using the volume key. Therefore, you can also take a picture using the volume key on your headphones!
And even better: if you have a Bluetooth headset, you don't even need to be near the phone at all. You can just prop it up against something, or use a handy iPhone tripod, stand back, and shoot the picture.