function check( img ) {
	
	if(img.height > 125){
		var ch = img.height;
		var cw = img.width;
		var h = 120;
		var w = (cw * h) / ch;
		img.height = h;
		img.width  = w;
		img.style.width = w;
	}
}

function img(){
	for(var i=0 ; i < 5 ; i++){
		var id = "product_img_" + i;
		var img = document.getElementById(id);
		check( img );
	}
}