I noticed that it appears that the ringtones and background images are not being referenced in the same folder location as the 7900 series phones. Typically on the UC520 the ringtones are stored in the flash:/ringtones..folder and the images are stored in Desktops/xxx folder.
Where are those ringtones and images stored on the SPA series phones, in particular 525G?
You can connect a USB storage to your PC and create a directory named 'pictures' on the USB device and copy the image files into that directory. The image files must be between 30K and 300K in size the phone will be able to read 45 images from the USB device. Connect the USB device to the Cisco SPA525G/525G2. Next, press the setup button, user preferences, screen preferences, wallpaper. Scroll to the image you would like to use.