Yeah, that was posted here a few times and it's actually a Japanese head that was put on a disabled Japanese tank by US soldiers in WW2:Just ran across something interesting... Riggs based the original Eddie painting (which later wound up as the debut album cover) on a photo of a decapitated US soldier's rotting head hanging from a Vietnamese tank. Here's the photo:
http://time.com/3518085/life-behind-the-picture-skull-on-a-tank-guadalcanal-1942/