Как насчет этого:
jQuery.fn.resizeImgByArea = function(avgDimension){
var $this = $(this),
oldW = $this.width(),
oldH = $this.height(),
RatiO = new Number(oldW/oldH),
newH = new Number(Math.round(Math.sqrt(avgDimension/RatiO))),
newW = new Number (Math.round(newH * RatiO));
$this.css({
width: newW + 'px',
height: newH + 'px'
});
}
$(document).ready(function() {
$('#images img').each(function(){$(this).resizeImgByArea(10000)});
});