From the menu in the top left, hit "Creative Corner" then "Create New Work". Choose "Create Art" since you want to post a photo. That will take you to a screen where you can provide a title, description, etc, but there's also a button for "Upload Your Art". Clicking this will bring up a small button to "Choose File". On my phone, at least, after allowing it to access my files and whatnot, I was provided with the options to choose between my Camera, Camcorder, and Documents. For a photo on the phone, choose "Documents" as this will bring up a directory of pretty much every image file on your phone. Once you're done, scroll down and hit "Create Art". Voila!