B

<div class="img-wrap">
	<img id="cvs-src" src="your-image.jpg" />
	<canvas width=500 height=500></canvas>
</div> 
 
<script>
	(function() {
		var supportsCanvas = !!document.createElement('canvas').getContext;
		supportsCanvas && (window.onload = greyImages);
 
		function greyImages() {
			var ctx = document.getElementsByTagName("canvas")[0].getContext('2d'),
				img = document.getElementById("cvs-src"),
				imageData, px, length, i = 0,
				grey;
 
			ctx.drawImage(img, 0, 0);
 
			// Set 500,500 to the width and height of your image.
			imageData = ctx.getImageData(0, 0, 500, 500);
			px = imageData.data;
			length = px.length;
 
			for ( ; i < length; i+= 4 ) {
				grey = px[i] * .3 + px[i+1] * .59 + px[i+2] * .11;
				px[i] = px[i+1] = px[i+2] = grey;
			}
 
			ctx.putImageData(imageData, 0, 0);
		}
	})();
</script>