How to change the background images on the all phones. The way I usually do this is below.
Make sure the image file is uploaded to the CUCM. It works only if we lock down the feature that allows to change the image from the phone. I used Common Phone Profile:
“Enable End User Access to Phone Background Image Setting” should be unchecked:
Once the Common Phone Profile is ready, use Bulk Administration to update this setting on all/group of phones: