ul.thumb {
                float: left;
                list-style: none;
                margin: 0; padding: 5px;
                width: 800px;
}
ul.thumb li {
                margin: 0; padding: 5px;
                float: left;
                position: relative;  
                width: 190px;
                height: 180px;
}
ul.thumb li img {
                width: 190px;
                height: 180px;
                -ms-interpolation-mode: bicubic; /* IE Fix for Bicubic Scaling */
                position: absolute;
                left: 0; top: 0;
                border:none;
}

ul.thumb li img:hover {
                background:transparent url(images/thumb_bg.png) no-repeat center;  
    border: none;
}