Décor is a System extension which allows you to replace the boring desktop pattern with a background picture of your choice. Décor handles StartupScreen, PICT, GIF and JPEG files. It has a lot of great features; for instance, you can ask it to select pictures from a certain folder, and to pick a new one every 10 minutes.
Décor is now free.
Décor works fine under MacOS 7, 8 and 9. (Under 8.0 and 8.1, you must disable the Desktop Pictures control panel. Under 8.5.x, you need to press "Remove Picture", then "Set Desktop" in the Appearance control panel.) Décor improves over MacOS's builtin features: it has random picking, automatic replacement, scriptability, etc.
If you use Kaleidoscope, you will need to turn off its "Desktop Pattern" option, otherwise Décor will not be able to work.
Décor won a honorable mention at the 1995 MacUser Shareware Awards.
The last version of Décor is 3.0.4. It is available in four languages: English, French, German, and Japanese. Each file weighs approximately 700K. These are the original versions, still carrying shareware registration instructions. You can now ignore them.
Concerning the Japanese translation, I received invaluable help from many Japanese users of Décor. Thanks to all of them, and in particular to Tadashi Kawaguchi. Thanks to Karl-Peter Kämpf for the German translation..