The following snippet below will display the original Image size in new window when clicking on the image thumbnail using JavaScript..
JAVASCRIPT FUNCTION
<script type="text/javascript" language="javascript">
function DisplayNewImageInWidnow()
{
var img = document.getElementById('<%= Image1.ClientID %>').src;
html = "<HTML><HEAD><TITLE>Photo</TITLE>"
+ "</HEAD><BODY LEFTMARGIN=0 "
+ "MARGINWIDTH=0 TOPMARGIN=0 MARGINHEIGHT=0><CENTER>"
+ "<IMG src='"
+ img
+ "' BORDER=0 NAME=image "
+ "onload='window.resizeTo(document.image.width,document.image.height)'>"
+ "</CENTER>"
+ "</BODY></HTML>";
popup= window.open ('','image', 'toolbar=0,location=0,directories=0,menuBar=0,scrollbars=0,resizable=1');
popup.document.open();
popup.document.write(html);
popup.document.focus();
popup.document.close();
}
</script>
ASPX Image Control MARKUP
<asp:Image ID="Image1" width="100px" height ="100px" runat="server" ImageUrl = "Images/PublicPrivateChart.gif" onclick="DisplayNewImageInWidnow();"/>
Happy Coding!