不要override了,就自己新建一个属性吧,
[Bindable(false)] 
        [Category("Appearance")] 
        [DefaultValue("")] 
        [Localizable(true)] 
        public System.Drawing.Image ImageUrl 
        { 
            get 
            { 
                return (ViewState["BackIMG"]==null?string.empty:(string)ViewState["BackIMG"]);
            } 
            set 
            { 
                ViewState["BackIMG"]= value;             } 
        } protected override void AddAttributesToRender(HtmlTextWriter writer)
{
    string backIMG=(string)ViewState["BackIMG"];
    if(!string.IsNullOrEmpty(backIMG))
    {
      writer.AddStyleAttribute(HtmlTextWriterStyle.BackGroundImage,ResolveURL(backIMG));
    }
}
大致如此了,具体的方法名和参数名我也没有记清楚