我個人覺得，這個js（頭像，圖片）上傳，立即展示，對做web前端的童鞋來說，還是非常有用的。

主要的js    previewImage.js:

function PreviewImage(obj, imgPreviewId, divPreviewId) {
	var allowExtention = ".jpg,.bmp,.gif,.png"; //,允許上傳檔案的字尾名
	var extention = obj.value.substring(obj.value.lastIndexOf(".") + 1).toLowerCase();
	var browserVersion = window.navigator.userAgent.toUpperCase();
	if (allowExtention.indexOf(extention) > -1) {
		if (browserVersion.indexOf("MSIE") > -1) {
			if (browserVersion.indexOf("MSIE 6.0") > -1) {//ie6
				document.getElementById(imgPreviewId).setAttribute("src", obj.value);
			} else {//ie[7-8]、ie9
				obj.select();
				var newPreview = document.getElementById(divPreviewId + "New");
				if (newPreview == null) {
					newPreview = document.createElement("div");
					newPreview.setAttribute("id", divPreviewId + "New");
					newPreview.style.width = 160;
					newPreview.style.height = 170;
					newPreview.style.border = "solid 1px #d2e2e2";
				}
				newPreview.style.filter = "progid:DXImageTransform.Microsoft.AlphaImageLoader(sizingMethod='scale',src='" + document.selection.createRange().text + "')";
				var tempDivPreview = document.getElementById(divPreviewId);
				tempDivPreview.parentNode.insertBefore(newPreview, tempDivPreview);
				tempDivPreview.style.display = "none";
			}
		} else if (browserVersion.indexOf("FIREFOX") > -1) {//firefox
			var firefoxVersion = parseFloat(browserVersion.toLowerCase().match(/firefox\/([\d.]+)/)[1]);
			if (firefoxVersion < 7) {//firefox7以下版本
				document.getElementById(imgPreviewId).setAttribute("src", obj.files[0].getAsDataURL());
			} else {//firefox7.0+                    
				document.getElementById(imgPreviewId).setAttribute("src", window.URL.createObjectURL(obj.files[0]));
			}
		} else if (obj.files) {
			//相容chrome、火狐等，HTML5獲取路徑                   
			if (typeof FileReader !== "undefined") {
				var reader = new FileReader();
				reader.onload = function (e) {
					document.getElementById(imgPreviewId).setAttribute("src", e.target.result);
				}
				reader.readAsDataURL(obj.files[0]);
			} else if (browserVersion.indexOf("SAFARI") > -1) {
				alert("暫時不支援Safari瀏覽器!");
			}
		} else {
			document.getElementById(divPreviewId).setAttribute("src", obj.value);
		}
	} else {
		alert("僅支援" + allowSuffix + "為字尾名的檔案!");
		obj.value = ""; //清空選中檔案
		if (browserVersion.indexOf("MSIE") > -1) {
			obj.select();
			document.selection.clear();
		}
		obj.outerHTML = obj.outerHTML;
	}
}
 

	<div class="news_img">
		<label for="newCover" class="ncLabel">配圖：</label>
		<img id="imgView" src=""  alt="" />
    		<input type="file" name="file1" class="file"  value='瀏覽...' onchange="PreviewImage(this,'imgView','pic_preview')" />
	</div>

基本就是這樣的了。