webView.backgroundColor = UIColor.clearColor()
for subView in webView.subviews {
if subView.isKindOfClass(UIScrollView) {
for shadow in subView.subviews {
if shadow.isKindOfClass(UIImageView){
shadow.hidden = true
}
}
}

}

必须要设置backgroundColor = UIColor.clearColor() 不然也是没效果的