Here's a mini-poster of Derri I created from a photo I took at Cornerstone 2002.
Here's a 18x24 poster I created from Lost Dogs photos I took at Cornerstone 2001. Download it, take it to your local copy shop, and they can print it out for you.
PC Users: Right click on the appropriate link and choose "Set as Wallpaper." Alternatively, you can save it on your computer and then change your Display Properties to point to the new background.
Mac Users: control-click the appropriate link, save it somewhere on your computer, then use the Appearance control panel to put the image on your desktop.
These are based on the aforementioned poster.
Here's another set of backgrounds of a picture of the three Dogs together.