The "Background properties" dialog allows you to define settings for the background of the slide.

Same background as preceding object.

If this option is selected, the slide will have no background definition  but will use the same background as the previous slide:

Select a new background

If this option is selected, the slide will have its own background definition. In that case, the following zones set properties for the background.
Solid brush Selects a plain color.
Gradient 2 colors Selects a gradient of 2 colors
Gradient 3 colors Selects a gradient of 3 colors
Image from library Selects a background image from the library
Remark: By default, the library contains a dozen of background screens.
You can get additionals backgrounds installing the Texturemate extension from this page Download extensions
Image disk Allows you to select a photo or an image.
File Indicates the name of the current file
Allow you to selects an image file
Keep aspect ratio If this box is checked, then the image will not be deformed, and:
Open the Image framing and correction dialog to regulate framing and image corrections
Full filling Allows the image to fill the whole screen with image deformation as needed.