Right-click on the image and copy the image location, not the link. Then click on the "Insert Media" button above and paste the location.
Sometimes (not in all browsers) it also works when you simply highlight, with your mouse, a smiley you see on another webpage, press CTRL+C and then CTRL+V right here in WGT's edit window.
The reason those links do not work for you, Gaoerfuqiu, is that this site's discussion forum and its software seem to be an innovative, in-house solution, not the standard discussion forums like phpBB or vBulletin, where the codes given by you would work. (And the methods that work here wouldn't work there.)
PS: I ain't no "WGT master", I've only been (hyper-)active in the forums.