I recently upgraded to a new iMac and felt it was time to change the default background image to something more “me”. I found a few articles and thought I would post the details too.

Firstly you will need to have the image you want to use and note the name of it (name-of-image.jpg)

Note that changing the default logon image has to be done using terminal as the files are locked in to the root user, unless of course you are logged in to the Mac using the root login.

So open Terminal from the Applications/Utilities folder and you are ready to go.

If you want to keep the old image then it needs to be renamed so enter the following line in to the terminal window

sudo mv /System/Library/CoreServices/DefaultDesktop.jpg /System/Library/CoreServices/DefaultDesktop.jpg.old

You will be asked for the password so just enter it and press enter.

sudo cp /path/to/image name-of-image.jpg /System/Library/CoreServices/DefaultDesktop.jpg

WEnter your password again and then the next time you log in the new screen will be there.

Alternatively there is little app that can do this if you are not to sure about using Terminal.

Head over to loginox and see if this is for you