Setup for Matching Desktop Images Changing at Login on Dual Monitors

This allows you to have identical or paired images changing at intervals such as at login. It is not a random image changing process as I have not found a way to do that, but if you have a lot of desktop images available it is a similar effect. This method is tested on PowerPCs using OS X 10.5.8, but may work on other Macs.

1. Create two folders, say DIL and DIR, for the left hand desktop images and the right hand desktop images.
2. Put a single image into one of these folders, make the name start with "1 X" (where X is an optional suffix such as "image") and make a copy of that image in the other folder also. Both images should have the same name.
3. Open System Preferences, Desktop & Screen Saver and set up for multiple monitors. This will open two windows, "Desktop & Screen Saver" for the main monitor (the one with the menu) and "Desktop Picture" for the secondary monitor
4. On the main monitor select the Desktop tab then click + to add the folder DIL (assuming your main monitor is your left monitor). Click on the image within (1 X.jpg)to set this as the desktop image for the left monitor, then tick Change picture and select "When Logging In" from the pull down menu. Leave Random order unticked.
5. Repeat step 4 for the right hand monitor using folder DIR. Close System Preferences.
6. Create all the other images you want the desktops to use each time you log in. Name these "2 X", "3 X", "4 X", etc. and put them in a folder DIL Temp. Duplicate this folder and rename it DIR Temp. You should have four folders (DIL, DIL Temp, DIR and DIR Temp)
7. Log out then log in again holding down the shift key. This will deactivate the automatic login items to save time. The desktop should still be the same image (1X.jpg)
8. Open System Preferences, Desktop & Screen Saver, select the folders DIL and DIR as the desktop image sources. i.e. the select folders, not the images within them. Close System Preferences.
9. Log out, then log in again holding down the shift key. The desktop should still be the same image (1X.jpg)
10. Drag a second image from DIL Temp into DIL. (i.e 2X.jpg) Drag a second image also named 2X.jpg) from DIR Temp into DIR. Close System Preferences.
11. Log out, then log in again holding down the shift key. The desktop should now be the second image i.e. 2.jpg on both monitors
12. Drag all the other images from DIL Temp into DIL and also place identical copies with identical names in DIR by dragging them from the DIR Temp folder
13. When you click into the System Preferences window you will see the folders DIL and DIR fill with the other images. i.e. it should then refresh itself. Close System Preferences.
14. Log out, then log in again holding down the shift key. The desktop should now be the third image i.e. 3.jpg. It this is the case, then the setup is complete and working

Now your two monitors are set to have image 3 X as the desktop, but when you next log in this will change and they will have 4 X as the desktop. I have taken shortcuts and found the result unsuccessful, with mis-matched images on the two monitors, so I would recommend that you follow all of the instructions to be safe.

The same process can be used to have different images which are part of a wider image (e.g. a panorama) appear on both monitors. To do this have the left hand half of the panorama named 1 X in folder DIL and have the right hand half of the panorama named 1 X in the folder DIR.