img src 改变问题

<script type="text/javascript">
function changeSrc(){
if(document.getElementById("pic").src=="images/5.jpg")
{
document.getElementById("pic").src="images/6.jpg";

}
if(document.getElementById("pic").src="images/6.jpg")
{
document.getElementById("pic").src="images/5.jpg";
}
}
</script>

<img id="pic" align="center" margin-right="10px" src="images/6.jpg" width="25%" onclick="return changeSrc()"/>

点击图像只能改变一次图像显示，想要改变多次则把代码改写为其他的

<script type="text/javascript">
function changeSrc(){
var element=document.getElementById("pic");
if(element.src.match("images/5.jpg"))
{
element.src="images/6.jpg";
}else{
element.src="images/5.jpg";
}
}
</script>

<img id="pic" align="center" margin-right="10px" src="images/6.jpg" width="25%" onclick="return changeSrc()"/>

再次进行优化，当有多个图片进行切换时，怎么确定是那个图片，如下可以这么做

<script type="text/javascript">
function changeSrc(dom){
var myid=dom.getAttribute("id");
var element=document.getElementById(myid);
if(element.src.match("images/5.jpg"))
{
element.src="images/6.jpg";
}else{
element.src="images/5.jpg";
}
}
</script>

<img id="pic11" align="center" margin-right="10px" src="images/6.jpg" width="25%" onclick="changeSrc(this)"/>

<img id="pic12" align="center" margin-right="10px" src="images/6.jpg" width="25%" onclick="changeSrc(this)" />