Images must be uploaded at administrator level in smarten, then only it will be available for the dashboard or object.
Solution :
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.