gForm.DrawImage(bmp, 10, 10, bmp.Width, bmp.Height);
this.Invoke(new EventHandler(delegate { gForm.DrawImage(bmp, 10, 10, bmp.Width, bmp.Height); }));
this.Invoke(new DoUpdateForm(UpdateForm), bmp);
[...]
private delegate void DoUpdateForm(Bitmap bmp);
private void UpdateForm(Bitmap bmp)
{
}