<asp:imagebutton id="ImageButton1" runat="server" onclick="ImageButton1_Click" xmlns:asp="#unknown" />
protected void ImageButton1_Click(object sender, EventArgs e)
{
MessageBox.Show("You clicked on image!");
}
Javascript =>
s.Append("<img src='images/print2.gif' border='0' style='cursor: hand;' onclick='onclicked()'>");
s.Append("<script type='text/javascript'>function onclicked(){alert('You clicked on image');}</script>")
I tested & working for me =)
Hope it helps.