由于代码很简单，这里就闲话不多说了，直接上代码，小伙伴们自己研读代码就明白了。

前台代码： 

代码如下:
/*修改头像*/ 
    //上传 
    function _sc() { 
        $(".ckfile").html("").css("color", "#535353"); 
        $("#_userImgPath").val(""); 
        var str = $("#file").val(); 
        if ($.trim(str) == "") { 
            $(".ckfile").html("请选择文件。").css("color", "red"); 
            return false; 
        } 
        else { 
            var postfix = str.substring(str.lastIndexOf(".") + 1).toUpperCase(); 
            if (postfix == "JPG" || postfix == "JPEG" || postfix == "PNG" || postfix == "GIF" || postfix == "BMP") { 
                $('#showimg').attr('src', 'Images/loading.gif').attr("title", "上传中，请稍后…"); 
                var path = "Upload/UserImg"; 
                $.ajaxFileUpload({ 
                    url: '/Upload.aspx?path=Upload|UserImg&shape=100*100', 
                    secureuri: false, 
                    fileElementId: 'file', 
                    dataType: 'text', 
                    success: function (msg) { 
                        if (msg.lastIndexOf(path) == -1) { 
                            $(".ckfile").html(msg).css("color", "red"); 
                        } 
                        else { 
                            $('#showimg').attr('src', msg).attr("title", "我的头像"); 
                            $("#_userImgPath").val(msg); 
                        } 
                    } 
                }); 
            } else { 
                $(".ckfile").html("文件格式错误。").css("color", "red"); 
                return false; 
            } 
        } 
    } 

后台代码：

代码如下:
using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Web; 
using System.Web.UI; 
using System.Web.UI.WebControls; 
using SS.Upload; 
using WFC.Fenxiao; 
namespace wanfangcheng 
{ 
    public partial class Upload : BasePage 
    { 
        //文件大小 1024 kb 
        private long size = 1024; 
        //文件类型 
        private string type = ".jpg|.jpeg|.png|.gif|.bmp"; 
        //保存名称 
        string name = ""; 
        //保存路径 
        private string path = @"Upload/UserImg"; 
        //保存大小 
        private string shape = "100*100"; 
        protected void Page_Load(object sender, EventArgs e) 
        { 
            HttpFileCollection files = Request.Files; 
            if (files != null && files.Count > 0) 
            { 
                name = BaseRole.Instance.UserId.ToString(); 
                if (Request.QueryString["size"] != null) 
                { 
                    size = Convert.ToInt32(Request.QueryString["size"]); 
                } 
                if (Request.QueryString["path"] != null) 
                { 
                    path = Request.QueryString["path"].ToString().Trim().Replace('|', '/'); 
                } 
                if (Request.QueryString["name"] != null) 
                { 
                    name = Request.QueryString["name"].ToString().Trim(); 
                } 
                if (Request.QueryString["shape"] != null) 
                { 
                    shape = Request.QueryString["shape"].ToString().Trim(); 
                } 
                uploadMethod(files); 
            } 
        } 
        /// <summary> 
        /// 上传图片 
        /// </summary> 
        /// <param name="hc"></param> 
        public void uploadMethod(HttpFileCollection hc) 
        { 
            HttpPostedFile _file = hc[0]; 
            //文件大小 
            long _size = _file.ContentLength; 
            if (_size <= 0) 
            { 
                Response.Write("文件错误。"); 
                Response.End(); 
                return; 
            } 
            if (size * 1024 < _size) 
            { 
                Response.Write("文件过大,最大为" + size + "KB。"); 
                Response.End(); 
                return; 
            } 
            //文件名 
            string _name = _file.FileName; 
            //文件格式 
            string _tp = System.IO.Path.GetExtension(_name).ToLower(); 
            if (type.IndexOf(_tp) == -1) 
            { 
                Response.Write("文件格式错误。"); 
                Response.End(); 
                return; 
            } 
            //保存路径 
            string _path = HttpContext.Current.Server.MapPath(path) + @"/" + name + _tp; 
            try 
            { 
                int w = Convert.ToInt32(shape.Split('*')[0]); 
                int h = Convert.ToInt32(shape.Split('*')[1]); 
                ImageHelper.CutForCustom(_file, _path, w, h, 50); 
                Response.Write(path + @"/" + name + _tp); 
            } 
            catch (Exception) 
            { 
                Response.Write("哎呦，出错了。"); 
                Response.End(); 
            } 
        } 
    } 
} 

是不是很实用，也很简单易懂呢，以上是自己项目中使用的代码，小伙伴们如果发现有问题的地方，还请告之。谢谢