Images must be uploaded at administrator level in smarten, then only it will be available for the dashboard or object.
To use images in background of any Objects or in Dashboards:
Go to Administration -> Upload Images then browse files from your system.
We are supporting JPEG, JPG, GIF and PNG files.
Note: This article is based on Smarten Version 5.0. This may or may not be relevant to the Smarten version you may be using.