.square {
    float:left;
    position: relative;
    width: 100px;
    padding-bottom : 100px; /* = width for a 1:1 aspect ratio */
    margin:1.66%;
    background-position:center center;
    background-repeat:no-repeat;
    background-size:cover; /* you change this to "contain" if you don't want the images to be cropped */
}

       
.img_1{background-image:url('2014/hongkong/1.jpg');}
       
.img_2{background-image:url('2014/hongkong/2.jpg');}
       
.img_3{background-image:url('2014/hongkong/3.jpg');}
       
.img_4{background-image:url('2014/hongkong/4.jpg');}
       
.img_5{background-image:url('2014/hongkong/5.jpg');}
       
.img_6{background-image:url('2014/hongkong/6.jpg');}
       
.img_7{background-image:url('2014/hongkong/7.jpg');}
       
.img_8{background-image:url('2014/hongkong/8.jpg');}
       
.img_9{background-image:url('2014/hongkong/9.jpg');}
       
.img_10{background-image:url('2014/hongkong/10.jpg');}
       
.img_11{background-image:url('2014/hongkong/11.jpg');}
       
.img_12{background-image:url('2014/hongkong/12.jpg');}
       
.img_13{background-image:url('2014/hongkong/13.jpg');}
       
.img_14{background-image:url('2014/hongkong/14.jpg');}
       
.img_15{background-image:url('2014/hongkong/15.jpg');}
       
.img_16{background-image:url('2014/hongkong/16.jpg');}
       
.img_17{background-image:url('2014/hongkong/17.jpg');}
       
.img_18{background-image:url('2014/hongkong/18.jpg');}
       
.img_19{background-image:url('2014/hongkong/19.jpg');}
       
.img_20{background-image:url('2014/hongkong/20.jpg');}
       
.img_21{background-image:url('2014/hongkong/21.jpg');}
       
.img_22{background-image:url('2014/hongkong/22.jpg');}
       
.img_23{background-image:url('2014/hongkong/23.jpg');}
       
.img_24{background-image:url('2014/hongkong/24.jpg');}
       
.img_25{background-image:url('2014/hongkong/25.jpg');}
       
.img_26{background-image:url('2014/hongkong/26.jpg');}
       
.img_27{background-image:url('2014/hongkong/27.jpg');}
       
.img_28{background-image:url('2014/hongkong/28.jpg');}
       
.img_29{background-image:url('2014/hongkong/29.jpg');}
       
.img_30{background-image:url('2014/hongkong/30.jpg');}
       
.img_31{background-image:url('2014/hongkong/31.jpg');}
       
.img_32{background-image:url('2014/hongkong/32.jpg');}
       
.img_33{background-image:url('2014/hongkong/33.jpg');}
       
.img_34{background-image:url('2014/hongkong/34.jpg');}
       
.img_35{background-image:url('2014/hongkong/35.jpg');}
       
.img_36{background-image:url('2014/hongkong/36.jpg');}
       
.img_37{background-image:url('2014/hongkong/37.jpg');}
       
.img_38{background-image:url('2014/hongkong/38.jpg');}
       
.img_39{background-image:url('2014/hongkong/39.jpg');}
       
.img_40{background-image:url('2014/hongkong/40.jpg');}
       
.img_41{background-image:url('2014/hongkong/41.jpg');}
       
.img_42{background-image:url('2014/hongkong/42.jpg');}