ASP.NET

public partial class _Default : System.Web.UI.Page
{
    ArrayList imagenes = new ArrayList();

    protected void Page_Load(object sender, EventArgs e)
    {

        if (!Page.IsPostBack)
        {
            ImageButton ib3 = new ImageButton();
            ib3.ID = "ib3";
            ib3.ImageUrl = "Puesta de sol.jpg";
            ib3.Click += new ImageClickEventHandler(ImageButton_Click);
            ib3.Width = new Unit(100, UnitType.Pixel);
            ib3.Height = new Unit(100, UnitType.Pixel);
            form1.Controls.Add(ib3);
            imagenes.Add(ib3);

            Session["Imagenes"] = imagenes;
        }
        else
        {
            imagenes = (ArrayList)Session["Imagenes"];
            foreach (ImageButton ib in imagenes)
                form1.Controls.Add(ib);
        }
    }

    protected void ImageButton_Click(object sender, ImageClickEventArgs e)
    {
        Page.ClientScript.RegisterStartupScript(GetType(), null, "alert('HEY');", true);
    }
}