Is There A Perfect Web Design Width?
http://www.fivefingercoding.com/web-design/is-there-a-perfect-web-design-width

I tend to stick with fixed-width layouts, a 960px web design width in particular. It reduces the effects of the visitor x-factor and it’s just about perfect for any website.

Valuable article about website width and a rationale behind 960px wide.

参考に

naturalWidthとnaturalHeightは知らなかった。Imageオブジェクトのonloadが無難。

imageのwidth,height