JS 实现图片直接下载

<a href="picName.jpg"   id=pic1 onclick="savepic();return false;"style="cursor:hand">点击下载</a>   

<script type="text/javascript">

function savepic() {            if (document.all.a1 == null) {                objIframe = document.createElement("IFRAME");                document.body.insertBefore(objIframe);                objIframe.outerHTML = "<iframe name=a1 style='width:400px;hieght:300px' src=" + imageName.href + "></iframe>";                re = setTimeout("savepic()", 1)            }            else {                clearTimeout(re)                pic = window.open(imageName.href, "a1")                pic.document.execCommand("SaveAs")                document.all.a1.removeNode(true)            }        } 

</script>