判断img的src为空/点击时候两张图片来回替换

  if($('.icon-right img').src==null){
        $('.span-gray').addClass('c8');
    }

<img>

/////////////

<script>
function change_pic(){
var imgObj = document.getElementById("caocao_pic");
if(imgObj.getAttribute("src",2)=="images/caocao.png"){
imgObj.src="images/diaochan.png";
}else{
imgObj.src="images/caocao.png";
}
}
</script>
<img src="images/caocao.png" class="wujiang_pic_size" id="caocao_pic" onClick="change_pic()">