If you wish to set a custom background image, please raise a support ticket. We'll need a URL which is accessible on the public internet without a username or password. We will then set all trio's within your Tenant ID to use this URL as the background image. For example:
Dimensions of the screen/background image: 1920x1080
Top bar height: 120 pixels
Bottom bar height: 70 pixels
Note: Only .png and .jpeg files are supported.