So using Chrome - Inspect Element on an Image .. you can see the HTMLImageElement has a set of properties:

http://lh3.ggpht.com/_Y8FtTHDiOgY/SdKr_9Ol4ZI/AAAAAAAAAMM/YGjbra_plDM/s1024/Image_Properties.JPG

Also here is a web article talking about how to check naturalHeight using JavaScript:

http://javascript.royh.cn/img/naturalheight-2-0-naturalwidth.html