(hier klicken für eine deutsche Variante des Artikels: windows 7 wallpaper per RSS)

There is a tiny extension in Windows 7 (and Windows Server 2008 R2) that
allows to set the desktop background based on an RSS feed with pictures. See this one for an example:
Wallpaper Windows 7 Preview. This
results in a long running diashow with maybe one change of the picture per day.
The wallpapers can be delivered by an RSS feed. RSS stands for Really-Simple-Syndication.
This will feed your PC with pictures.

That's how it works:

Step 1: Subscribe to a feed

Use the Internet Explorer to click one of the following feeds, depending
on screen resolution:
Feed 1920×1200
Feed 1920×1080

The feed will be shown as follows:

Click on "Subscribe to this feed" and confirm the subscription in the
following dialog.

Step 2: Show Feed Properties

Great, the subscription was done. Now it is necessary to go a llitle bit
deeper into the operating system. View the feed properties is the next thing
to do.

Check "Automatically download attached files" as it is shown in the next
picture. Then you need to view the files!

Hmm, it is greyed out – the trick is to press ok to close the dialog (confirm
the question "would you like to download the attached files for the curretn feed
content") and then open it again using "view feed properties". Then "View files"
will be available.

"View files" leads to an explorer view of the attached pictures. This is
necessary because we need to know about the location of the files. Click
into the adress bar with the right mouse key and then on "copy adress as
text".

Step 3: Finally configure the Desktop Background

This step leads us into the control panel. Please remember that the
location of the files is still stored in the clipboard.

"Choose your desktop background" offers the "Browse" button. This is the
place to paste the file location using CTRL-V. A bit of finetuning can be
done using the other options. For example have a look at the frequency
("change picture every 30 min…"). The "Picture Position" determines how to
deal with pictures that don't have the exact resolution of the display.

Finished!

Just two additional hints::

Management of the feeds is done within the Internet Explorer Favorites.
In case some changes are necessary use this menu option.

Finally: there is the function "Next desktop background" in the contect
menu of the desktop (right mouse click on the desktop).

In case you can't wait to see the next picture…

Have fun!