How can i prevent a person from changing the desktop background or wallpaper on my computer ?
I want that nobody should be able to change the settings like background wallpapers on my computer . Is there a way to disable the wallpaper option so that nobody changes my personal settings.

Either don’t allow them to get on your computer or password protect your account and set them up an account with limited privileges.
You can do this from Control Panel > Users
or Control Panel > Administrative Tools
if you want more control over what they can and can’t do.
Generally no. If you let someone use your computer, it gives them full access to anything. Setup a 2nd user on your computer, set a password on the 2 accounts. This way if a friend needs to use your computer, they can set their own settings, and not disturb yours.
Here’s a good place for free wallpapers:
http://www.thispictures.com