change permissions to copy pictures into backgrounds

[compdoc]

> What is the try, that will allow me to do so?

Not sure I followed everything you were saying, but if you need to copy or
modify system files, (or root owed files) type into a term window: gksu
nautilus &

Also useful:  gksu gedit &  

The '&' allows the process to run in the background, although Nautilus does
not let go of the term window.