function grayscale(imgObj)
{
	var canvas = document.createElement('canvas');

	var canvasContext = canvas.getContext('2d');

	var imgW = imgObj.width;

	var imgH = imgObj.height;
	canvas.width = imgW;
	canvas.height = imgH;
	canvasContext.drawImage(imgObj, 0, 0);

	var imgPixels = canvasContext.getImageData(0, 0, imgW, imgH);

	for(var y = 0; y < imgPixels.height; y++){
	     for(var x = 0; x < imgPixels.width; x++){
	          var i = (y * 4) * imgPixels.width + x * 4;
	          var avg = (imgPixels.data[i] + imgPixels.data[i + 1] + imgPixels.data[i + 2]) / 3;
	          imgPixels.data[i] = avg;
	          imgPixels.data[i + 1] = avg;
	          imgPixels.data[i + 2] = avg;
	     }
	}
	canvasContext.putImageData(imgPixels, 0, 0, 0, 0, imgPixels.width, imgPixels.height);

	imgObj.parentNode.parentNode.insertBefore(canvas, imgObj.parentNode.parentNode.firstChild);
	
	return canvas.toDataURL();
}