setAttribute(name,value)

<script type="text/javascript">
//<!-[CDATA [

function imgfn() {
	var div1 = document.getElementById("div1");
	var img = document.images[0];

	img.setAttribute("width", "200");
	img.setAttribute("alt", "This was an image");
	var imgStr = "src = "+ img.getAttribute("src") + "<br />" + 
	"width = "+ img.getAttribute("width") + "<br />" +
	"alt = "+ img.getAttribute("alt") + "<br />" +
	"align = "+ img.getAttribute("align");
	div1.innerHTML = imgStr;
}
//]]>
</script>
<img src="dotty.gif" width="100" alt="an image" align="left" />
<input type="button" value="확인" onclick="imgfn();" />
<div id="div1"></div>

-- IE


-- FF