How To Dynamic Control Some Picture's Size By Javascript

i have some pictures in a page. there are have difference sizes. some
of them are too widen for be arrange in a line. so
i been tried to adject their sizes to more suitable.

i add a event to that image likes:
<img id="img" onLoad="adjustSize(this)" src="123.jpg">

and write a function in javascript:
function adjustSize(obj){
if (obj.width>250){
sizeRate=250/obj.width;
obj.width=obj.width*sizeRate;
if (obj.hight>268)
obj.hight=268;
}}

but exactly,i can get the image's width and height. cuz the loading
hasn't finished while the function of adjustSize works.