A new update to the game's website includes a program that let's you create your team of 4 heroes, give it name, and pick a background. Then, it will create an image that you can use for your desktop image. They only have a small amount of heroes you can use at the moment, but they have been slowly revealing the characters.
Here is the site.
Click on the 5th button on the little menu that says "Team Builder"
I think it's cool, and new backgrounds are always fun.