Here you go:
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>bluantinoo CSS Grayscale Bg Image Sample</title>
<style type="text/css">
div {
border: 1px solid black;
padding: 5px;
margin: 5px;
width: 600px;
height: 600px;
float: left;
color: white;
}
.grayscale {
background: url(yourimagehere.jpg);
-moz-filter: url("data:image/svg+xml;utf8,<svg xmlns=\'http://www.w3.org/2000/svg\'><filter id=\'grayscale\'><feColorMatrix type=\'matrix\' values=\'0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0\'/></filter></svg>#grayscale");
-o-filter: url("data:image/svg+xml;utf8,<svg xmlns=\'http://www.w3.org/2000/svg\'><filter id=\'grayscale\'><feColorMatrix type=\'matrix\' values=\'0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0\'/></filter></svg>#grayscale");
-webkit-filter: grayscale(100%);
filter: gray;
filter: url("data:image/svg+xml;utf8,<svg xmlns=\'http://www.w3.org/2000/svg\'><filter id=\'grayscale\'><feColorMatrix type=\'matrix\' values=\'0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0\'/></filter></svg>#grayscale");
}
.nongrayscale {
background: url(yourimagehere.jpg);
}
</style>
</head>
<body>
<div class="nongrayscale">
this is a non-grayscale of the bg image
</div>
<div class="grayscale">
this is a grayscale of the bg image
</div>
</body>
</html>
Tested it in FireFox, Chrome and IE. I've also attached an image to show my results of my implementation of this.
EDIT: Also, if you want the image to just toggle back and forth with jQuery, here's the page source for that...I've included the web link to jQuery and and image that's online so you should just be able to copy/paste to test it out:
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>bluantinoo CSS Grayscale Bg Image Sample</title>
<script src="http://code.jquery.com/jquery-1.11.0.min.js"></script>
<style type="text/css">
div {
border: 1px solid black;
padding: 5px;
margin: 5px;
width: 600px;
height: 600px;
float: left;
color: white;
}
.grayscale {
background: url(http://www.polyrootstattoo.com/images/Artists/Buda/40.jpg);
-moz-filter: url("data:image/svg+xml;utf8,<svg xmlns=\'http://www.w3.org/2000/svg\'><filter id=\'grayscale\'><feColorMatrix type=\'matrix\' values=\'0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0\'/></filter></svg>#grayscale");
-o-filter: url("data:image/svg+xml;utf8,<svg xmlns=\'http://www.w3.org/2000/svg\'><filter id=\'grayscale\'><feColorMatrix type=\'matrix\' values=\'0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0\'/></filter></svg>#grayscale");
-webkit-filter: grayscale(100%);
filter: gray;
filter: url("data:image/svg+xml;utf8,<svg xmlns=\'http://www.w3.org/2000/svg\'><filter id=\'grayscale\'><feColorMatrix type=\'matrix\' values=\'0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0.3333 0.3333 0.3333 0 0 0 0 0 1 0\'/></filter></svg>#grayscale");
}
.nongrayscale {
background: url(http://www.polyrootstattoo.com/images/Artists/Buda/40.jpg);
}
</style>
<script type="text/javascript">
$(document).ready(function () {
$("#image").mouseover(function () {
$(".nongrayscale").removeClass().fadeTo(400,0.8).addClass("grayscale").fadeTo(400, 1);
});
$("#image").mouseout(function () {
$(".grayscale").removeClass().fadeTo(400, 0.8).addClass("nongrayscale").fadeTo(400, 1);
});
});
</script>
</head>
<body>
<div id="image" class="nongrayscale">
rollover this image to toggle grayscale
</div>
</body>
</html>
EDIT 2 (For IE10-11 Users): The solution above will not work with the changes Microsoft has made to the browser as of late, so here's an updated solution that will allow you to grayscale (or desaturate) your images.
<svg>_x000D_
<defs>_x000D_
<filter xmlns="http://www.w3.org/2000/svg" id="desaturate">_x000D_
<feColorMatrix type="saturate" values="0" />_x000D_
</filter>_x000D_
</defs>_x000D_
<image xlink:href="http://www.polyrootstattoo.com/images/Artists/Buda/40.jpg" width="600" height="600" filter="url(#desaturate)" />_x000D_
</svg>
_x000D_