Please add the image behind http://kde-look.org/content/show.php/Larry+the+%28Cave%29Cow?content=18639 (the no-text version, two resolutions offered) to "Gentoo Linux Wallpapers" on http://www.gentoo.org/main/en/graphics.xml Thanks!
If you can find that source image, and if it's a compatible license, then sure. I think people are just hacking together their own Larry head from some other graphic; I have no idea where it originally comes from.
To my best knowledge the head of Larry the cow originates from small letter "s" of font "Font Heads" up at <http://www.fonthead.com/fonts/Font-Heads>. Click "License" on that page to see its EULA. (I'd provide a direct link, but it's not easy to get one.) The wallpaper is licensed as <http://creativecommons.org/licenses/by-nc-sa/2.0/>.
Wallpaper added, closing.