Yes, there has been a slide-show type wallpaper(s) for Linux for a while available over at gnome-look.org (Just search for animated under the wallpaper section). But now it comes as one of the options for Karmic (Ubuntu 9.10). The process is a simple one if you want to make your own. I will break down the method they used to create the cosmic slide-show that comes default with Karmic.
First, if you go to /usr/share/backgrounds you will see a folder named cosmos. Inside the folder, you will find an xml file and the 9 images that rotate every 30 minutes.
If you want to create your own, I suggest that you create your own folder within your $HOME/Pictures directory. (I do not condone copying files to your root directories when it is not necessary.
Select the images that you want to use, and decide how often you want them to rotate (you will need to know how many seconds that this is so grab a calculator to do the math). Below is the xml file that controls the cosmos wallpapers.

<background>
  <starttime>
    <year>2009</year>
    <month>08</month>
    <day>04</day>
    <hour>00</hour>
    <minute>00</minute>
    <second>00</second>
  </starttime>
<!-- This animation will start at midnight. -->
  <static>
    <duration>1795.0</duration>
    <file>/usr/share/backgrounds/cosmos/cloud.jpg</file>
  </static>
  <transition>
    <duration>5.0</duration>
    <from>/usr/share/backgrounds/cosmos/cloud.jpg</from>
    <to>/usr/share/backgrounds/cosmos/comet.jpg</to>
  </transition>
  <static>
    <duration>1795.0</duration>
    <file>/usr/share/backgrounds/cosmos/comet.jpg</file>
  </static>
  <transition>
    <duration>5.0</duration>
    <from>/usr/share/backgrounds/cosmos/comet.jpg</from>
    <to>/usr/share/backgrounds/cosmos/earth-horizon.jpg</to>
  </transition>
  <static>
    <duration>1795.0</duration>
    <file>/usr/share/backgrounds/cosmos/earth-horizon.jpg</file>
  </static>
  <transition>
    <duration>5.0</duration>
    <from>/usr/share/backgrounds/cosmos/earth-horizon.jpg</from>
    <to>/usr/share/backgrounds/cosmos/blue-marble-west.jpg</to>
  </transition>
  <static>
    <duration>1795.0</duration>
    <file>/usr/share/backgrounds/cosmos/blue-marble-west.jpg</file>
  </static>
  <transition>
    <duration>5.0</duration>
    <from>/usr/share/backgrounds/cosmos/blue-marble-west.jpg</from>
    <to>/usr/share/backgrounds/cosmos/galaxy-ngc3370.jpg</to>
  </transition>
  <static>
    <duration>1795.0</duration>
    <file>/usr/share/backgrounds/cosmos/galaxy-ngc3370.jpg</file>
  </static>
  <transition>
    <duration>5.0</duration>
    <from>/usr/share/backgrounds/cosmos/galaxy-ngc3370.jpg</from>
    <to>/usr/share/backgrounds/cosmos/helix-nebula.jpg</to>
  </transition>
  <static>
    <duration>1795.0</duration>
    <file>/usr/share/backgrounds/cosmos/helix-nebula.jpg</file>
  </static>
  <transition>
    <duration>5.0</duration>
    <from>/usr/share/backgrounds/cosmos/helix-nebula.jpg</from>
    <to>/usr/share/backgrounds/cosmos/jupiter.jpg</to>
  </transition>
  <static>
    <duration>1795.0</duration>
    <file>/usr/share/backgrounds/cosmos/jupiter.jpg</file>
  </static>
  <transition>
    <duration>5.0</duration>
    <from>/usr/share/backgrounds/cosmos/jupiter.jpg</from>
    <to>/usr/share/backgrounds/cosmos/sombrero.jpg</to>
  </transition>
  <static>
    <duration>1795.0</duration>
    <file>/usr/share/backgrounds/cosmos/sombrero.jpg</file>
  </static>
  <transition>
    <duration>5.0</duration>
    <from>/usr/share/backgrounds/cosmos/sombrero.jpg</from>
    <to>/usr/share/backgrounds/cosmos/whirlpool.jpg</to>
  </transition>
  <static>
    <duration>1795.0</duration>
    <file>/usr/share/backgrounds/cosmos/whirlpool.jpg</file>
  </static>
  <transition>
    <duration>5.0</duration>
    <from>/usr/share/backgrounds/cosmos/whirlpool.jpg</from>
    <to>/usr/share/backgrounds/cosmos/cloud.jpg</to>
  </transition>
</background>

To make it your own, copy the xml file, replace the file names to the path of the pictures, and there you have it, or you can continue reading to where I have disected another “animated” slide-show wallpaper.


If you want to look at one that hasn’t been “installed” I suggest downloading the MacAnimated wallpaper pack from gnome-look (Use the first download link, it doesn’t try to sell you anything or really make you wait a long amount of time). After you have the tar.gz file downloaded, extract it (don’t install it) and you can see the xml file in all it’s un-installed glory. (All the install SHOULD do is copy the files over into usr/share/backgrounds.)
I decided to test out to see if I could get the slide-show to work using the MacAnimated wallpapers, WITHOUT having to copy/move the files into /usr/share/backgrounds.
First I edited the xml file to change the directory of where it should look for the files. Here is the original xml file:
<!-- Based on Fedora Animated. Put together by zeeleck -->
<!-- backgrounds created by El-Sato -->
<background>
  <starttime>
    <hour>0</hour>
    <minute>00</minute>
    <second>01</second>
  </starttime>
<!-- + 12 am -->
<static>
<duration>18000.0</duration>
<file>/usr/share/backgrounds/MacAnimated/night.svg</file>
</static>
<!-- +5 am -->
<transition type="overlay">
	<duration>10800.0</duration>
	<from>/usr/share/backgrounds/MacAnimated/night.svg</from>
	<to>/usr/share/backgrounds/MacAnimated/sunrise.svg</to>
</transition>
<!-- +8 am -->
<transition type="overlay">
	<duration>7200.0</duration>
	<from>/usr/share/backgrounds/MacAnimated/sunrise.svg</from>
	<to>/usr/share/backgrounds/MacAnimated/day.svg</to>
</transition>
<!-- +10 am -->
<static>
	<duration>25200.0</duration>
	<file>/usr/share/backgrounds/MacAnimated/day.svg</file>
</static>
<!-- +5 pm -->
<transition type="overlay">
	<duration>7200.0</duration>
	<from>/usr/share/backgrounds/MacAnimated/day.svg</from>
	<to>/usr/share/backgrounds/MacAnimated/sunset.svg</to>
</transition>
<!-- +7pm -->
<transition type="overlay">
	<duration>7200.0</duration>
	<from>/usr/share/backgrounds/MacAnimated/sunset.svg</from>
	<to>/usr/share/backgrounds/MacAnimated/night.svg</to>
</transition>
<!-- +9pm -->
<static>
	<duration>10800.0</duration>
	<file>/usr/share/backgrounds/MacAnimated/night.svg</file>
</static> 
</background>

to

<!-- Based on Fedora Animated. Put together by zeeleck -->
<!-- backgrounds created by El-Sato -->
<background>
  <starttime>
    <hour>0</hour>
    <minute>00</minute>
    <second>01</second>
  </starttime>
<!-- + 12 am -->
<static>
<duration>18000.0</duration>
<file>/home/your username/Pictures/MacAnimated/night.svg</file>
</static>
<!-- +5 am -->
<transition type="overlay">
	<duration>10800.0</duration>
	<from>/home/your username/Pictures/MacAnimated/night.svg</from>
	<to>/home/your username/Pictures/MacAnimated/sunrise.svg</to>
</transition>
<!-- +8 am -->
<transition type="overlay">
	<duration>7200.0</duration>
	<from>/home/your username/Pictures/MacAnimated/sunrise.svg</from>
	<to>/home/your username/Pictures/MacAnimated/day.svg</to>
</transition>
<!-- +10 am -->
<static>
	<duration>25200.0</duration>
	<file>/home/your username/Pictures/MacAnimated/day.svg</file>
</static>
<!-- +5 pm -->
<transition type="overlay">
	<duration>7200.0</duration>
	<from>/home/your username/Pictures/MacAnimated/day.svg</from>
	<to>/home/your username/Pictures/MacAnimated/sunset.svg</to>
</transition>
<!-- +7pm -->
<transition type="overlay">
	<duration>7200.0</duration>
	<from>/home/your username/Pictures/MacAnimated/sunset.svg</from>
	<to>/home/your username/Pictures/MacAnimated/night.svg</to>
</transition>
<!-- +9pm -->
<static>
	<duration>10800.0</duration>
	<file>/home/your username/Pictures/MacAnimated/night.svg</file>
</static> 
</background>

Just right click on your desktop, select change appareance, click Add (+), and be sure to click All Files on the bottom right and select your xml file. It will work, and your don’t have to “install” it to your system. Happy Wallpaper Animating/Slide-Show-ing!
(This was just a pre-made example that I broke apart. You can truly take any images you want, with any time frame you want to have them change at. Remember, reverse engineering something fairly simple can teach you some things. :))