How can I completely disable desktop background change?

I need to block the possibility for a single user to change the desktop background, or at least to make it possible only by inserting his password on OS X Lion / Mountain Lion.

I want to lock every possibility, from iPhoto to Safari…

Solution 1:

One possible solution would be to set the permissions on ~/Library/Preferences/com.apple.desktop.plist to be read-only for the user.

Solution 2:

Found a way to stop background changing.

1. Rename /System/Library/Services/Set\ Desktop\ Picture.workflow Change the extension. This stops right clicking a photo to set desktop picture.
2. Safari: Add 3 files in ~/Library/Safari named
   Safari Desktop Picture.jpg
   Safari Desktop Picture.jpeg
   Safari Desktop Picture.png
   change permissions and lock the 3 files.
   Stops from changing it in Safari.
3. Firefox download menu editor and take the options out.