Character portraits, icons, and background images are unlocked through normal gameplay. For example, playing a certain number of matches, leveling up, and using certain characters in game modes.
The fastest way to get all 3 of these achievements is to start a game on Practice Mode. This will unlock a character portrait, and an Icon. There are 4 extra background images unlocked from the start of the game.
Quit to main menu, select Bonus Features -> Hero Card -> Customize. Select a character portrait aside from the default, do the same with your icon and background image. Press to back out, save your changes, and the achievements will unlock.