C#

//Attach this to the MouseMove event of pic1
void pic1_MouseMove(object sender,MouseEventArgs e) {
  if(e.Button == Windows.Forms.MouseButtons.Left && !dragging) {
    dragging = true;
    pic1.DoDragDrop(pic1.Image,DragEffect.Move);
  }
}

//Attach this to the DragOver event of pic1
void pic2_DragOver(object sender,DragEventArgs e) {
  e.Effect = DragEffect.None;

  if(e.Data.GetDataPresent(typeof(Bitmap)) {
    e.Effect = DragEffect.Move;
  }
}

//Attach this to the DragDrop event of pic2
void pic2_DragDrop(object sender,DragEventArgs e) {
  if(e.Data.GetDataPresent(typeof(Bitmap)) {
    Bitmap img = (Bitmap)e.Data.GetData(typeof(Bitmap));
    pic2.Image = img;

    dragging = false;
  }
}