Change background picture position in Fedora 18

Ok, yesterday I installed Fedora 18 on my notebook and I found something strange. I didnt have the option to change the display type of the background-picture on the desktop. Thats really strange, I like that my desktop to have a nice, stretched picture but without those options, I had only a scaled picture ( or, I dont know the default!). So it wasnt so nice!
I searched on the Internet for some answer at this problem and I found a script in PyGtk that do that kind of job. But why to use/create a script in PyGtk for this when I can create a bash script ( Im a fan of terminal commands!)? And its convenient for me a bash script cause I dont want to execute that Python script every time I change my background-picture and I really dont need a  GUI for that. So why to use PyGtk? Why to have a script of 300 lines of codes when you can have only 30 lines! So, its a difference!
And, I fire up terminal and Vim and this is what Ive done: