It's supposed to work on any Power Macintosh with Mac OS 7.6 or higher with Applescript installed and active. I've been able to test it only on few configurations. It's a shareware. MyPicture Screensaver is just an application, so launch it and leave it in the background. It could be a good idea to put an alias of it in the Startup Items folder of your System folder.
Many settings are available.
This window has two main parts. The password you've typed will be asked each time you will deactivate the screensaver. Paste the picture of your choice here or drop it from another application. You can drop here any image file that QuickTime can understand. In the MyPicture Screensaver Settings dialog, you can now click on the picture to set the background color.