C# Definition:

    [ComVisible(true)]
    [ComImport]
    [Guid("DE5BF786-477A-11D2-839D-00C04FD918D0")]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    public interface IDragSourceHelper {
    void InitializeFromBitmap(
        [In, MarshalAs(UnmanagedType.Struct)] ref ShDragImage dragImage,
        [In, MarshalAs(UnmanagedType.Interface)] IDataObject dataObject);

    void InitializeFromWindow(
        [In] IntPtr hwnd,
        [In] ref Point pt,
        [In, MarshalAs(UnmanagedType.Interface)] IDataObject dataObject);
    }

User-Defined Types:

    [StructLayout(LayoutKind.Sequential)]
    public struct ShDragImage {
    public Size sizeDragImage;
    public Point ptOffset;
    public IntPtr hbmpDragImage;
    public Color crColorKey;
    }

Notes: