How to save html5 canvas image to SQL Server - asp.net

Question

I found this code on aspsnippets.com. I ran it successfully as far as running web page and being able to draw a signature and then it saves it to another html image on the screen. But I want to get this image into my database. How can I call html from my .aspx.vb page?
<div class="tools">
Marker <a href="#colors_sketch" data-tool="eraser">
Eraser</a>
</div>
<br />
<canvas id="colors_sketch" width="500" height="200" style = "border:3px solid #ccc">
</canvas>
<br />
<br />
<input type="button" id="btnSave" value="Save as Image"/>
<hr />
<img id = "imgCapture" alt = "" style = "display:table-cell;border:1px solid #ccc" />
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.8.3/jquery.min.js"></script>
<script src="http://intridea.github.io/sketch.js/lib/sketch.min.js" type="text/javascript"></script>
<script type="text/javascript">
$(function () {
$('#colors_sketch').sketch();
$(".tools a").eq(0).attr("style", "color:#000");
$(".tools a").click(function () {
$(".tools a").removeAttr("style");
$(this).attr("style", "color:#000");
});
$("#btnSave").bind("click", function () {
var base64 = $('#colors_sketch')[0].toDataURL();
$("#imgCapture").attr("src", base64);
$("#imgCapture").show();
});
});
</script>