img.bigimg { height: 100%; width: 100%; }
<img src="путь до картинки" class="bigimg">
#hat_center {background-image:url('/images/hat.jpg');height:125px;margin:0 3px 0 0px;}
#hat_center { background-image: url ('/images/hat.jpg') no-repeat fixed; height: 125px; margin: 0 3px 0 0px; }