#foo {width: 300px; height: 400px; overflow: hidden;}

<div id="foo"></div>

this.someimage = randomImageUrl;
$("foo").innerHTML = "<img src='"+this.someimage+"' class='fooimage' />";

Now, the picture could be 200x200 or 1100x400 ... it's totally random. I can just stretch it (or reduce its size) by using:

.fooimage {width: 300px; height: 400px;}

$("foo").innerHTML = "<img src='"+this.someimage+"' class='fooimage' />";

Or I could test its size:

imgHeight = newImg.height; 
imgWidth = newImg.width;

... and maybe something like this:

if(imgHeight >400){
   $("foo").innerHTML = "<img src='"+this.someimage+"' height='400' />";
}

and browsers will do the rest.

But there must be something better. Any ideas? Thanks! :)