terminal command which set background a picture

Why don't you just change the wallpaper via System Preferences > Desktop & Screensaver? There's even an option to change the wallpaper in the pop up menu when you ctrl-click or right-click anywhere on the Desktop.

floba

One way to do this is to create a folder and use the Desktop & Screen Saver Preferences, in the Desktop tab, to select that folder and specify "Change picture every ..." minutes or seconds. Then all you have to do from the command line is to copy files to that folder to display them and remove them when you're done.

the easiest way to do that is using apple script as follows:

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tell application "System Events"
-- SET DESKTOP TO SPECIFIC PICTURE
tell current desktop
set picture rotation to 0 -- (0=off, 1=interval, 2=login, 3=sleep)
set picture to file "Mac OS X:Library:Desktop Pictures:Plants:Agave.jpg"
end tell
end tell

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you can call an apple script from a shell script using osascript command. You can also directly embed it into a shell script using osascript with -e switch.

If you get a "permission denied" message, just enter "sudo " before the command.
You'll need to enter an administrator password.