Then you need to open the info menu for this directory, so you step one directory up and then do that, and you need to open the key and enter your admin user name (there is only the system user by default). Why do that? Because it won’t allow you to change the filename or do anything in this folder, even if you add the user to the file itself. You need to put it to the directory. Then you can rename the old file, and put a new one from your desktop images and give it the name DefaultDesktop.jpg.

Then you restart and see the new one. I have done it and it works.

This fixed my blue screen problem and now I have the background picture I want.”

THANK YOU Patrick! This resolved my problem. Any one else having trouble with the blue screen give this a try.

1. Make sure the file IS a jpg – just checking the file extention is not enough
open your image editor/viewer/metadata editor and make sure it states “JPEG”

2. the 72 DPI issue, was not my case but worth to check, same solution as 1.

3. permitions/location: make sure the file is in the default location “/system/library/coreservices/defaultdesktop.jpg” – to reset use the instructions above in the comments.

I was very annoyed with this issue, but thanks to the clues you guys gave, I fixed it on my end, Hope you can also.

This fixed my blue screen problem and now I have the background picture I want.

Fahad

sudo defaults write /Library/Preferences/com.apple.loginwindow DesktopPicture “/Path/to/picture/you/want/to/use/image.jpg”

approach, I think that path has to be a file in the root system. I tried it to a picture in my /Users/myhome dir and it didn’t work until I moved it to a file outside my home. (I just put it in /System/Library/CoreService )

I’m probably wrong, but no clue why it didn’t work to the file in my home dir (I don’t think I had the path wrong either.)

http://usingmac.com/2007/11/6/leopard-change-login-background

So I created a script…

#!/bin/bash
declare -a files
let count=0
IFS=$'\n'
for i in `find -E /Users/dturner/Pictures/Wallpaper/mandolux -iregex ". \/[^\.][^\/] \.(jpg|jpeg)$"` ; do
files[$count]=$i
((count ))
done
N=${#files[@]}
((N=RANDOM%N))
randomfile=${files[$N]}
cp "$randomfile" /System/Library/CoreServices/DefaultDesktop.jpg

Then in Terminal I entered:
sudo edit /etc/crontab

And added a line so it looks like:

# The periodic and atrun jobs have moved to launchd jobs
# See /System/Library/LaunchDaemons
#
# minute hour mday month wday who command
* */1 * * * root /Users/dturner/scripts/new_login_wallpaper 2>&1 /dev/null

…Now my default login background changes every hour!