Computer lab of 30 Mac

Go to System Preferences > Keyboard > Shortcuts. In the left pane select Services, then in the right pane under Pictures, uncheck the item Set Desktop Picture.

Then, while still in System Preferences, go to the menu at the top of your screen (next to the Apple) and select View > Customize and uncheck the Keyboard prefs pane. That will prevent users from undoing the change you made.

You should probably also block the Desktop & Screen Saver prefs pane.

Since you have a lab, you should consider using Apple Remote Desktop to manage your Macs.

After doing the above, here is another thing you might consider doing ...

Consider enabling Parental Controls on the student accounts to customize (aka limit) what students may do with the lab Macs. For example, you can completely block access to System Preferences and other applications you don't want students to use.

There's quite a bit of customization possible in Parental Controls.

Of course, to do this each Mac needs to have at least 2 accounts ... an admin account that only you can use + a student (standard user) account. (For ease of management, the account names & passwords could be the same on all the lab Macs. Depends on the overall implementation in your lab.)

Apart from setting control, screen sharing can be used to remotely login to each Mac.

Also, have a look at whether the macOS guest account could be useful. A shared folder for each user could be set up. How to Set Up Network File Sharing on macOS, Without Sharing Your Username and Password could also be helpful.

- Pie Lover

Hi there troyfifi,

Thanks for contacting Apple Support Communities. We're happy to help. We understand you'd like to lock down the ability to change the desktop picture.

You can go to System Preferences > Keyboard > Keyboard Shortcuts.

Select Services in the left pane.

Then, in the right pane uncheck the item "Set Desktop Picture" in the Pictures section.

This should help.

Have a nice day!