It would also be common to add sample UI on top of your images, so that clients and others can see your work in context. The quickest way to do this would be to buy a PNG or Illustrator overlay or take an hour or two and make one yourself – I've gone ahead and made them for you! You can find them in the Resources folder, including the Illustrator file they were made with so you can modify the text, add profile images, etc. Of course, if you want the challenge, go ahead and make them yourself from scratch!