alert in the run time of an image

<script type="text/javascript">
    
        function HideDiv() 
        { 
            if (document.getElementById) 
            { // DOM3 = IE5, NS6 
                document.getElementById('myDiv').style.visibility = 'hidden'; 
            } 
            else 
            { 
                if (document.layers) 
                { // Netscape 4 
                    document.hideShow.visibility = 'hidden'; 
                } 
                else 
                { // IE 4 
                    document.all.hideShow.style.visibility = 'hidden'; 
                } 
            } 
        }
        
        function ShowDiv() 
        { 
            if (document.getElementById) 
            { // DOM3 = IE5, NS6 
                document.getElementById('myDiv').style.visibility = 'visible'; 
            } 
            else 
            { 
                if (document.layers) 
                { // Netscape 4 
                    document.hideShow.visibility = 'visible'; 
                } 
                else 
                { // IE 4 
                    document.all.hideShow.style.visibility = 'visible'; 
                } 
            }
        }
    
</script>

<img src="C:\myPic.jpg" onclick="ShowDiv()" width="100px" height="100px" />
<div id="myDiv" style="visibility:hidden; background-color:Blue; z-index:100" >
<asp:Label ID="lblQuestion" runat="server" Text="Do you want to delete image?"></asp:Label>
<asp:Button ID="btnYes" runat="server" Text="Yes" OnClick="btnYes_Click" />
<asp:Button ID="btnNo" runat="server" Text="No" OnClientClick="HideDiv()" />
</div>

protected void btnYes_Click(object sender, EventArgs e)
{
     System.IO.File.Delete("C:\\myPic.jpg");
}