RibbonX kennt .NET Images

<dropDown id="MyDropDown"
          getItemID="getDDItemID"
          getItemCount="getDDItemCount"
          getItemLabel="getDDItemLabel"
          getItemImage="getDDItemImage"
          onAction="onDDAction">
</dropDown>

public stdole.IPictureDisp getDDItemImage(Office.IRibbonControl control, int index)
{
   MemoryStream iconStream = new MemoryStream(...);
   return ImageConverter.ImageToPictureDisp(Image.FromStream(iconStream));
}

internal class ImageConverter : System.Windows.Forms.AxHost
{
  public ImageConverter() : base(string.Empty) { }

  static public stdole.IPictureDisp ImageToPictureDisp(Image image)
  {
    return (stdole.IPictureDisp)GetIPictureDispFromPicture(image);
  }

  static public stdole.IPictureDisp IconToPictureDisp(Icon icon)
  {
    return ImageToPictureDisp(icon.ToBitmap());
  }
}

public Image getDDItemImage(Office.IRibbonControl control, int index)
{
   MemoryStream iconStream = new MemoryStream(...);
   return Image.FromStream(iconStream);  
}