Get the real width and height of an image with JavaScript? (in Safari/Chrome)

I am creating a jQuery plugin.

How do I get the real image width and height with Javascript in Safari?

The following works with Firefox 3, IE7 and Opera 9:

var pic = $("img")

// need to remove these in of case img-element has set width and height
pic.removeAttr("width"); 
pic.removeAttr("height");

var pic_real_width = pic.width();
var pic_real_height = pic.height();

But in Webkit browsers like Safari and Google Chrome values are 0.