Prevent users from changing wallpaper

Are you managing these computers in Workgroup manager? If so you could just create a new computer group and manage the system preference panes for all of them. If you click on a group of computers then go to system preferences, click manage always then hide the preferences you don't want them to have access to.

Set up an account (ideally on a machine with workgroup manager installed) with a background that you want. Ideally this will be an image that is on all of the machines you wish to manage. Using one of the predefined Apple images works. Log into workgroup manager and select the group or computer list you wish to manage. Click on the preferences for the group and then Details. Click on the plus side to add a new preference manage. Navigate to the ~/Library/Preferences folder of the account you had set up previously and then select the com.apple.desktop.plist file. By default the settings for this file (such as desktop image) are set to be managed Once. Meaning that they will be set when the user logs in but can be changed after that. To change this click on the settings you want to have managed all the time. Then click copy. Highlight the word Always and then paste. When asked if you want to replace the MCX settings select yes. Apply and done. Users will then all have the background you defined and will not able to change it via any method. Of course locking the desktop preference is a good move too.
My apologies if any of my wording is a little off as I'm not currently sitting in front of a computer with workgroup manager.

Well in that case! Here is my best attempt. It is basically a script that will allow you to replace the file via ftp, all you will have to do is enter the IP User and Password for each user, it will do the rest. Since you are managing the computers you will first have to turn on ssh and file sharing using ftp. Then assuming you have no terminal experience whatsoever do the following. Open up terminal and cd to a good directory to make a script in, I like using ~/Scripts/ a folder you will have to create if its not already there.

cd ~/Scripts/

Then once in ~/Scripts type:

nano ftpscript.sh

Then press enter. This will create the script file and open up nano which is a command line text editor. Now copy and paste this script into the window.

#!/bin/bash
+echo -n "enter ftp address"+
+read HOST+
+echo -n "enter User name"+
+read USER+
+echo -n "enter password"+
+read PASSWD+

+ftp -n $HOST <<END_SCRIPT+
+quote USER $USER+
+quote PASS $PASSWD+
+put ~/Library/Preferences/com.apple.desktop.plist ~/Library/Preferences/com.apple.desktop.plist
quit
END_SCRIPT
+exit 0+

Then press control (not apple) and x at the same time. Then type:
chmod 755 ftpscript.sh

now your script is ready and executable.

Before you execute the script set your desktop background to the background you want the students to have, and lock the com.apple.desktop.plist file.

Once all that is set you can type ./ftpscript.sh

Bada bing bada boom, it still leaves you with a entering in 400 user name IP and passwords, but if you have an admin account on all the computers you can replace that script with the one below which will only leave you entering in the IP for each comp.


#!/bin/bash
+echo -n "enter ftp address"+
+read HOST+
*USER=Put your admin user name here*
*PASSWD=Put your admin password here*

+ftp -n $HOST <<END_SCRIPT+
+quote USER $USER+
+quote PASS $PASSWD+
+put ~/Library/Preferences/com.apple.desktop.plist ~/Library/Preferences/com.apple.desktop.plist
quit
END_SCRIPT
+exit 0+


Hope this helps!
adam

Tom Rice wrote:
Set up an account (ideally on a machine with workgroup manager installed) with a background that you want. Ideally this will be an image that is on all of the machines you wish to manage. Using one of the predefined Apple images works. Log into workgroup manager and select the group or computer list you wish to manage. Click on the preferences for the group and then Details. Click on the plus side to add a new preference manage. Navigate to the ~/Library/Preferences folder of the account you had set up previously and then select the com.apple.desktop.plist file. By default the settings for this file (such as desktop image) are set to be managed Once. Meaning that they will be set when the user logs in but can be changed after that. To change this click on the settings you want to have managed all the time. Then click copy. Highlight the word Always and then paste. When asked if you want to replace the MCX settings select yes. Apply and done. Users will then all have the background you defined and will not able to change it via any method. Of course locking the desktop preference is a good move too.
My apologies if any of my wording is a little off as I'm not currently sitting in front of a computer with workgroup manager.

This seems like a better way, nice to know! Hopefully my script will be of some help if you do decide to lockdown the plist file