What you need
A Mac, running Mac OS X 10.1 or later, and Disk Copy (in /Applications/Utilities), together with tools for making the the folder window background.
Potential problems
There are few problems that can arise, except for errors using the command line when making the background graphic invisible. Disk Copy isn't completely free of bugs, and you should keep separate copies of each of the files involved. Early releases of OS X occasionally ignore or rebuild folder settings kept in the hidden .DS_Store file in each folder. This can result in quirky resizing of windows and other glitches. Thankfully, these have become uncommon as OS X matures.
Further info
Hints and detailed instructions for building different types of installation file are at Stepwise and there are other helpful hints at www.macosxhints.com.
Checklist• Build your desired background image and save as a JPEG file.
• Create a New Blank Image using Disk Copy, selecting the right size.
• Open the mounted disk image, and copy files and background picture to it.
• In Terminal, make a hidden folder and move the background picture into it.
• Open the View Options for the mounted disk image. Set icon size.
• Set the background picture, typing in the path - for example
/Volumes/MyDiskImage/.background/ - to find it.
• Complete setting up image, eject to write it, then check by remounting with Disk Copy.
Click 'Next Page' below for the step-by-step guide...Custom disk images