From Quandir Software:
Daydreamer will display a picture pointed to by a URL and update it as often as you like. You can do this with several pictures. You can have Daydreamer make time lapse movies of the URL picture, adding a new frame to a movie each time the picture is refreshed. You can also save the pictures to your computer automatically, allowing for use as Dsktop pictures and/or screensavers. Daydreamer is AppleScriptable. With sample scripts provided with the distribution, you can view slide shows of picture folders on your computer, make those slide shows into QuickTime movies, or receive an alert email when a picture changes.