Remote background channels are a subscription service to backgrounds hosted on a remote system which provides a person with a new background through a web service.
Subscription links are provided from the hosts for the background channels
Subscriptions are a type of XML RSS feeds with the suffix .bgchannel It's possible to use a uri:// scheme for this, of course people will probably complain against the additional URI. bgchannel://
For a demo background channel, see the Demo Page
When the person clicks on the link they they are prompted about subscribing to the background channel.
The evolution-webcal is a brain-dead simple program that does as URI register in GNOME for webcal:// URIs, this would probably be a good starting point for the GNOME URI system.
When the person has accepted the subscription to a background channel the channel appears in the background capplet as a background with the URL informtation included.
The URI of the bgchannel can be stored in the backgrounds XML file along with some extra meta-data like a friendly URL of the source. The Background Capplet uses an XML format for storing background locations which can be extended. A nice extra would be double clicking on the channel should open up the URL in your browser.
As the remote site updates the persons background changed to reflect the new backgrounds available
New backgrounds are checked for everyday at 8:00 AM? (actual time doesn't really matter too much) local time to the computer or 1 hour after session login. If a new background is available it is downloaded and replaces the old background.
A nice thing to do is to have a notification are icon appear when retrieving a new background and giving a link to the background channel web site so people can retrieve older backgrounds they may have liked. The notification are icon can remain around for an hour, grayed out after the download and replace is finished.