You can easily set any image as a device background. Just follow the instruction below:
Open Device settings dialog.
Click Theme (in the lower left corner) and Upload image.
Choose an image from your computer.
Wait until the image is uploaded and click the blue OK button to save your changes.
You can now either refresh Roombelt on your device or wait up to 30 seconds and the background will load automatically.
Background images that follow device orientation give the best results. If you put your tablet in a landscape orientation use horizontal background and if you have a device in a portrait orientation use vertical background.