Code

var mailIcon = null;

function onLinkCreated(sender, args)
{
	var link = args.getLink();
	link.setCustomDraw(1);
}

function onDrawLink(sender, args)
{
	var applet = <%= diagramView.AppletElement %>;
	if (!mailIcon)
		mailIcon = applet.loadImage("mail.png");

	if (mailIcon)
	{
		var link = args.getLink();
		var points = link.getControlPoints();
		var l = points.size() - 1;
		var start = points.get(0);
		var end = points.get(l);

		var w = mailIcon.getWidth(null) * 25.4 / 72;	// convert to mm
		var h = mailIcon.getHeight(null) * 25.4 / 72;
		var x = (start.getX() + end.getX() - w) / 2;
		var y = (start.getY() + end.getY()) / 2 + 4;

		args.getGraphics().drawImage(mailIcon, x, y, w, h, null);
	}
} 

Code

Graphics g = Graphics.FromImage(image);
...
g.DrawImage(image, leftCorner); 

Code

protected void Page_Load(object sender, EventArgs e)
{
	var diagram = diagramView.Diagram;
	if (!IsPostBack)
	{
		var node1 = diagram.Factory.CreateShapeNode(20, 20, 20, 20);
		var node2 = diagram.Factory.CreateShapeNode(120, 20, 20, 20);
		var link = diagram.Factory.CreateDiagramLink(node1, node2);
		link.CustomDraw = CustomDraw.Additional;
	}

	diagram.DrawLink += OnDrawLink;
}

void OnDrawLink(object sender, DrawLinkEventArgs e)
{
	var unit = diagramView.Diagram.MeasureUnit;
	var image = Image.FromFile(Server.MapPath("mail.png"));
	float imgWidth = image.Width * Constants.GetPixel(unit);
	float imgHeight = image.Height * Constants.GetPixel(unit);

	var link = e.Link;
	var pt1 = link.StartPoint;
	var pt2 = link.EndPoint;

	var leftCorner = new PointF((pt1.X + pt2.X - imgWidth) / 2, (pt1.Y + pt2.Y) / 2 + 4);
	e.Graphics.DrawImage(image, leftCorner);
}