img{                
    -moz-border-radius:24px; 
    -webkit-border-radius: 24px;
    border-radius: 24px;
    display:block;
}
div {
    border: 2px solid #c7c7c7; 
    border-radius: 24px;
    -webkit-border-radius: 24px;
    width:40px; /* the width of image */
    height:40px; /* the height of image */
}

演示：http://jsfiddle.net/EnmMp/1/