Selecting and storing the coordinates Diameter from an image

I have an image and I want that each time I click on the image, it stores the diamter 0.25cm around the point where it was clicked and stores the coordinates. 

I wrote a different code for this process but it uses asp:Literal plus it is a box and i dont know how to set the diameter so right now it selects the (x,y) coordinates. Also, the asp:literal box is visible to the user when clicking as a gridbox unless it doesnt store the coordinates. I do not want it to be visible. 

Can anyone help with this issue. 

This is my previous code. 

 xmlns="http://www.w3.org/1999/xhtml">  runat="server">     type="text/javascript"> function recordClick(col, row) { document.getElementById('TextboxClicked').value += "|" + col + "," + row; //window.alert("Clicked col: " + col + " row: " + row); }     id="form1" runat="server"> 
  style="width: 331px; height: 451px; background-image: url('Images/image1.jpg'); ">  runat="server" ID="LiteralDivs">   runat="server" ID="TextboxClicked" ClientIDMode="Static" TextMode="MultiLine" Width="400px" Height="41px"> />