There are many ways to make a background.
1) Smudging the render & using filters.
2) Using a stock photo.
3) Using the natural background of the image.
Examples:
1)Smudging
[Image: http://i837.photobucket.com/albums/zz297/AKB990/Signatures/HydraMeteor.jpg]
[Image: http://i837.photobucket.com/albums/zz297/AKB990/Signatures/Flowerz.jpg]
2)Stock Photo(s)
[Image: http://i837.photobucket.com/albums/zz297/AKB990/Signatures/Walkinthepark.jpg]
[Image: http://i837.photobucket.com/albums/zz297/AKB990/Signatures/SpacemanFull.jpg]
3)Natural Background(Like using a wallpaper)
[Image: http://i837.photobucket.com/albums/zz297/AKB990/Signatures/Hydrazone.jpg]
[Image: http://i837.photobucket.com/albums/zz297/AKB990/Signatures/MabinogiDragon.jpg]