If conventional wallpapers (in other words static ones) don`t convince you, then the next step is to install a dynamic animated wallpaper, like this Blood Curdling Halloween.
Blood Curdling Halloween will convert your desktop wallpaper into horrible blood-red colours and tones where in poor visibility (as if you were using a low definition camera) you can see an old haunted house with bats flying around. As if that wasn`t enough, every so often Death appears in a terrifying image, complete with his unmistakeable scythe.