protected virtual string ArrowUpImageUrlInternal { get { if (string.IsNullOrEmpty(ArrowUpImageUrl)) return Page.ClientScript.GetWebResourceUrl(this.GetType(), "skmControls2.ArrowUp.gif"); else return ArrowUpImageUrl; } }In my project I added the images under Images directory (in the original project they are in the same directory as the cs file). The cs file I added to App_Code folder.