Get natural img size.

gistfile1.js

imgNaturalSize($img, function (width, height) {
    // $img is now loaded
});

jquery.imgNaturalSize.js

function imgNaturalSize($img, callback) {
	if ($img[0].complete || $img[0].width && $img[0].height) {
		returnSize();
	} else {
		$img.load(function () {
			returnSize();
		});
	}
	
	function returnSize() {
		var img;
		
		if ('naturalWidth' in $img[0]) {
			callback($img[0].naturalWidth, $img[0].naturalHeight);
		} else {
			img = new Image();
			img.src = $img[0].src;
			callback(img.width, img.height);
		}
	}
}