Hi zhanae Tucker
We're afraid you can only post pictures if you're using a computer (desktop or laptop) to post. If you look at the message box, you'll see there is a little tree icon along the top (where all the other tools, like bold and the smiley face are, on the right). Click on this and Your Computer and you can upload a pic from your desktop.
We're working on getting the functionality to be able to post a pic from a phone and it shouldn't be too long now!