No problem mate. Usualy, you add a little texte at the bottom of the image "Center picture by [author]" so your user won't see it when they use it as a wallpaper (hided by the start menu) but can see where the image came from.
i'm sorry i replyed so late but i had a internet problem that irritated me alot
Now i'm online again and yes all thx to wonderfull life but how i do a credit? and where:d