var img = new Image();
img.onload = function() {
alert(this.width + 'x' + this.height);
}
img.src = 'http://www.google.com/intl/en_ALL/images/logo.gif';
// for the original width and height in px of the source
image.naturalWidth, image.naturalHeight
// for the image size in px rendered on the screen
image.width, image.height
image.width