first put all you images(jpg i assume) to a one folder and run the rename script to number the pics
http://blog.whatsupbuddy.com/uploads/rename download this file and give it execute permission

then download this file and edit the following parameters as you wish
http://blog.whatsupbuddy.com/uploads/add

dir=fedora #{the name of the folder}
size=121 #{the number of images}
duartion=120.0 #{the duration of the wallpaper in seconds}
transition=5.0 #{the duration of the transition in seconds}

and run the add file inside the image folder
then copy the image folder to /user/share/backgrounds
then open system-preferences-apperance and change the wallpaper to /user/share/backgrounds/{dir}/{dir}.xml

thats it