JavaScript code:

/**
 * Paints a gif on a canvas and replaces the original image with the canvas.
 * @param {Element} image Gif image that will be turned into a still canvas
 */
function freezeGif(image) {
	var canvas = document.createElement('canvas');
	var imageWidth = image.naturalWidth;
	var imageHeight = image.naturalHeight;
	canvas.width = image.naturalWidth;
	canvas.height = image.naturalHeight;
	canvas.getContext('2d').drawImage(image, 0, 0, imageWidth, imageHeight);
	// if possible, retain all css aspects
	for (var i = 0; i < image.attributes.length; i++) {
		canvas.setAttribute(image.attributes[i].name, image.attributes[i].value);
	}
	image.parentNode.replaceChild(canvas, image);
}