<script src="Scripts/jquery-1.4.2.min.js" type="text/javascript"></script>
<script src="Scripts/ajaxupload3.9.js" type="text/javascript"></script>

<style type="text/css">
#txtFileName {
width: 300px;
}
.btnsubmit{border-bottom: #cc4f00 1px solid; border-left: #ff9000 1px solid;border-top: #ff9000 1px solid; border-right: #cc4f00 1px solid;text-align: center; padding: 2px 10px; line-height: 16px; background: #e36b0f; height: 24px; color: #fff; font-size: 12px; cursor: pointer;}
</style>
上传图片：<input type="text" id="txtFileName" /><div id="btnUp" style="width:300px;" class=btnsubmit >浏览</div>
<div id="imglist"></div>

<script type="text/javascript">
$(function () {
var button = $('#btnUp'), interval;
new AjaxUpload(button, {
//action: 'upload-test.php',文件上传服务器端执行的地址
action: '/handler/AjaxuploadHandler.ashx',
name: 'myfile',
onSubmit: function (file, ext) {
if (!(ext && /^(jpg|jpeg|JPG|JPEG)$/.test(ext))) {
alert('图片格式不正确,请选择 jpg 格式的文件!', '系统提示');
return false;
}
// change button text, when user selects file
button.text('上传中');
// If you want to allow uploading only 1 file at time,
// you can disable upload button
this.disable();
// Uploding -> Uploading. -> Uploading...
interval = window.setInterval(function () {
var text = button.text();
if (text.length < 10) {
button.text(text + '|');
} else {
button.text('上传中');
}
}, 200);
},
onComplete: function (file, response) {
//file 本地文件名称，response 服务器端传回的信息
button.text('上传图片(只允许上传JPG格式的图片,大小不得大于150K)');
window.clearInterval(interval);
// enable upload button
this.enable();
var k = response.replace("<PRE>", "").replace("</PRE>", "");
if (k == '-1') {
alert('您上传的文件太大啦!请不要超过150K');
}
else {
alert("服务器端传回的串："+k);
alert("本地文件名称："+file);
$("#txtFileName").val(k);
$("<img />").appendTo($('#imglist')).attr("src", k);
}
}
});
});
</script> 

public void ProcessRequest(HttpContext context)
{
context.Response.ContentType = "text/plain";
HttpPostedFile postedFile = context.Request.Files[0];
string savePath = "/upload/images/";
int filelength = postedFile.ContentLength;
int fileSize = 163600; //150K
string fileName = "-1"; //返回的上传后的文件名
if (filelength <= fileSize)
{
byte[] buffer = new byte[filelength];
postedFile.InputStream.Read(buffer, 0, filelength);
fileName = UploadImage(buffer, savePath, "jpg");
}
context.Response.Write(fileName);
}
public static string UploadImage(byte[] imgBuffer, string uploadpath, string ext)
{
try
{
System.IO.MemoryStream m = new MemoryStream(imgBuffer);
if (!Directory.Exists(HttpContext.Current.Server.MapPath(uploadpath)))
Directory.CreateDirectory(HttpContext.Current.Server.MapPath(uploadpath));
string imgname = CreateIDCode() + "." + ext;
string _path = HttpContext.Current.Server.MapPath(uploadpath) + imgname;
Image img = Image.FromStream(m);
if (ext == "jpg")
img.Save(_path, System.Drawing.Imaging.ImageFormat.Jpeg);
else
img.Save(_path, System.Drawing.Imaging.ImageFormat.Gif);
m.Close();
return uploadpath + imgname;
}
catch (Exception ex)
{
return ex.Message;
}
}
public static string CreateIDCode()
{
DateTime Time1 = DateTime.Now.ToUniversalTime();
DateTime Time2 = Convert.ToDateTime("1970-01-01");
TimeSpan span = Time1 - Time2; //span就是两个日期之间的差额 
string t = span.TotalMilliseconds.ToString("0");
return t;
}

<script src="js/jquery-1.3.js"></script>
<script src="js/ajaxupload.3.5.js"></script> 

<ul> 
<li id="example"> 
<div id="upload_button">文件上传</div>
<p>已上传的文件列表:</p> 
<ol class="files"></ol>
</ul> 

$(document).ready(function(){
var button = $('#upload_button'), interval;
var fileType = "all",fileNum = "one"; 
new AjaxUpload(button,{
action: 'do/uploadfile.php',
/*data:{
'buttoninfo':button.text()
},*/
name: 'userfile',
onSubmit : function(file, ext){
if(fileType == "pic")
{
if (ext && /^(jpg|png|jpeg|gif)$/.test(ext)){
this.setData({
'info': '文件类型为图片'
});
} else {
$('<li></li>').appendTo('#example .files').text('非图片类型文件，请重传');
return false; 
}
}
button.text('文件上传中');
if(fileNum == 'one')
this.disable();
interval = window.setInterval(function(){
var text = button.text();
if (text.length < 14){
button.text(text + '.'); 
} else {
button.text('文件上传中'); 
}
}, 200);
},
onComplete: function(file, response){
if(response != "success")
alert(response);
button.text('文件上传');
window.clearInterval(interval);
this.enable();
if(response == "success");
$('<li></li>').appendTo('#example .files').text(file); 
}
});
}); 

<input type="file" name="userfile"> 

$upload_dir = '../file/';
$file_path = $upload_dir . $_FILES['userfile']['name'];
$MAX_SIZE = 20000000;
echo $_POST['buttoninfo'];
if(!is_dir($upload_dir))
{
if(!mkdir($upload_dir))
echo "文件上传目录不存在并且无法创建文件上传目录";
if(!chmod($upload_dir,0755))
echo "文件上传目录的权限无法设定为可读可写";
}
if($_FILES['userfile']['size']>$MAX_SIZE)
echo "上传的文件大小超过了规定大小";
if($_FILES['userfile']['size'] == 0)
echo "请选择上传的文件";
if(!move_uploaded_file( $_FILES['userfile']['tmp_name'], $file_path))
echo "复制文件失败，请重新上传"; 
switch($_FILES['userfile']['error'])
{
case 0:
echo "success" ;
break;
case 1:
echo "上传的文件超过了 php.ini 中 upload_max_filesize 选项限制的值";
break;
case 2:
echo "上传文件的大小超过了 HTML 表单中 MAX_FILE_SIZE 选项指定的值";
break;
case 3:
echo "文件只有部分被上传";
break;
case 4:
echo "没有文件被上传";
break;
}