Css 同比例缩小图片

/*控制图片的大小*/
.contentimg{
max-width:600px;
/*max-height:100px;*/
}
*html.contentimg{
width:e­xpression(this.width>50&&this.width>this.height?60:auto);
/*height:expresion(this.height>50?50:auto);
*/
}
调用
  $("#"+id.substring(0,id.length-5)+"arCon").html(msg);
                                   $("div.arCon img").each(function(){
                                        $(this).addClass("contentimg");
                                   });