The method james3v6 describes works for me, I use it all the time. I learned that method from clinkster. The key is to start with a popular template, or one of your own and hit "add Image" then make sure you are adding "Inside Current Image"
This method from MamaTriedRob also works, just started using it. Using MTR's method, you add the image below your existing line template.
imgflip.com/i/1bt7r8