Paso 1:Conseguir imágenes grandes que os gusten, mi caso;
Paso 2: Editar el archivo “.xml” que ordena automaticamente la transición de nuestras imágenes,
lo podemos encontrar en usr/share/backgraund/cosmos/background -1.xml (plantilla original)
podemos copiar su contenido, y dejar intacto el original, el mio quedo asi;
<background>
<starttime>
<year>2011</year>
<month>03</month>
<day>01</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/cool/dibujo.jpg</file>
</static>
<transition>
<duration>5.0</duration>
<from>/usr/share/backgrounds/cool/dibujo.jpg</from>
<to>/usr/share/backgrounds/cool/droidscollection.jpg</to>
</transition>
<static>
<duration>1795.0</duration>
<file>/usr/share/backgrounds/cool/droidscollection.jpg</file>
</static>
<transition>
<duration>5.0</duration>
<from>/usr/share/backgrounds/cool/droidscollection.jpg</from>
<to>/usr/share/backgrounds/cool/linux-technology.jpg</to>
</transition>
<static>
<duration>1795.0</duration>
<file>/usr/share/backgrounds/cool/linux-technology.jpg</file>
</static>
<transition>
<duration>5.0</duration>
<from>/usr/share/backgrounds/cool/linux-technology.jpg</from>
<to>/usr/share/backgrounds/cool/linux-tux-crystal.jpg</to>
</transition>
<static>
<duration>1795.0</duration>
<file>/usr/share/backgrounds/cool/linux-tux-crystal.jpg</file>
</static>
<transition>
<duration>5.0</duration>
<from>/usr/share/backgrounds/cool/linux-tux-crystal.jpg</from>
<to>/usr/share/backgrounds/cool/penguin.jpg</to>
</transition>
<static>
<duration>1795.0</duration>
<file>/usr/share/backgrounds/cool/penguin.jpg</file>
</static>
<transition>
<duration>5.0</duration>
<from>/usr/share/backgrounds/cool/penguin.jpg</from>
<to>/usr/share/backgrounds/cool/WDebian.jpg</to>
</transition>
<static>
<duration>1795.0</duration>
<file>/usr/share/backgrounds/cool/WDebian.jpg</file>
</static>
<transition>
<duration>5.0</duration>
<from>/usr/share/backgrounds/cool/WDebian.jpg</from>
<to>/usr/share/backgrounds/cool/gnulinux.jpg</to>
</transition>
<static>
<duration>1795.0</duration>
<file>/usr/share/backgrounds/cool/gnulinux.jpg</file>
</static>
<transition>
<duration>5.0</duration>
<from>/usr/share/backgrounds/cool/gnulinux.jpg</from>
<to>/usr/share/backgrounds/cool/kde.jpg</to>
</transition>
<static>
<duration>1795.0</duration>
<file>/usr/share/backgrounds/cool/kde.jpg</file>
</static>
<transition>
<duration>5.0</duration>
<from>/usr/share/backgrounds/cool/kde.jpg</from>
<to>/usr/share/backgrounds/cool/tux-world.jpg</to>
</transition>
<static>
<duration>1795.0</duration>
<file>/usr/share/backgrounds/cool/tux-world.jpg</file>
</static>
<transition>
<duration>5.0</duration>
<from>/usr/share/backgrounds/cool/tux-world.jpg</from>
<to>/usr/share/backgrounds/cool/dibujo.jpg</to>
</transition>
</background>