How to restrict changing desktop wallpaper?
I didn't find any way to prevent changing the desktop picture, but you could just change it back to the default every few seconds.

&lt;?xml version="1.0" encoding="UTF-8"?&gt;
&lt;!DOCTYPE plist PUBLIC -//Apple Computer//DTD PLIST
1.0//EN http://www.apple.com/DTDs/PropertyList-1.0.dtd&gt;
&lt;plist version="1.0"&gt;
&lt;dict&gt;
    &lt;key&gt;Label&lt;/key&gt;
    &lt;string&gt;com.stackexchange.apple.65938&lt;/string&gt;
    &lt;key&gt;ProgramArguments&lt;/key&gt;
    &lt;array&gt;
        &lt;string&gt;osascript&lt;/string&gt;
        &lt;string&gt;-e&lt;/string&gt;
        &lt;string&gt;tell application "Finder"
set f to POSIX file "/Library/Desktop Pictures/Galaxy.jpg"
if desktop picture is not file f then set desktop picture to f
end tell&lt;/string&gt;
    &lt;/array&gt;
    &lt;key&gt;StartInterval&lt;/key&gt;
    &lt;integer&gt;10&lt;/integer&gt;
&lt;/dict&gt;
&lt;/plist&gt;


Save the file above as /Library/LaunchAgents/com.stackexchange.apple.65938.plist, change the owner, and load the plist:

sudo chown root /Library/LaunchAgents/com.stackexchange.apple.65938.plist
sudo launchctl load /Library/LaunchAgents/com.stackexchange.apple.65938.plist


The property list is loaded automatically when users log in.