用css讓圖片可以置中且保持比例縮放於指定框尺寸

.frame {  
    height: 160px; /*can be anything*/
    width: 160px; /*can be anything*/
    position: relative;
}
img {  
    max-height: 100%;  
    max-width: 100%; 
    width: auto;
    height: auto;
    position: absolute;  
    top: 0;  
    bottom: 0;  
    left: 0;  
    right: 0;  
    margin: auto;
}