(If you use a Mac) I save my photo collages to my desktop then drag them into iPhoto. Then, I go to System Preferences, choose the folder with my photo collages, and use it as my screen saver. It's a round-about way to get what you want, but it works!
its very simple to make it ur background all u have to do is follow these simple instructions:
1.once u finish your image go to the corner that says"export" and click it
2.once u have done that just fill in the info of how you want it as your wallpaper
3. enjoy and amazing wallpaper that you will love
Picture Collage Maker for Mac
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use my pictures as a screen saver.