<body>
    <div>
        <form id="fileUpload" action="@Url.Action("AddImage")" method="POST" enctype="multipart/form-data">
            <input id="fileInput" type="file" />
            <input type="button" value="Upload file" id="btnFileUpload" />
        </form>
    </div>
    
    <script type="text/javascript">
            $("#btnFileUpload").click(function() {
                var formData = new FormData();
                var file = document.getElementById("fileInput").files[0];
                formData.append("fileInput", file);
                $.ajax({
                    url: "Home/AddImage",
                    type: "POST",
                    data: formData,
                    contentType: false,
                    processData: false,
                    success: function() {
                        alert("URA");
                    }
                });
            });
        
    </script>
</body>public ActionResult Index()
        {
            return View();
        }
        [HttpPost]
        public ActionResult AddImage(HttpPostedFileBase fileInput)
        {
            string fileName = fileInput.FileName;
            var image = new Bitmap(fileInput.InputStream, false);
            image.Save(Path.Combine(HttpContext.Server.MapPath("/Images/"), fileName));
            return View("Index");
        }      var fileE = document.getElementById("inputID");
        fileE.onchange = function () {
            var xhr = new XMLHttpRequest();
            xhr.open("POST", "/Home/Index");
            xhr.send(this.files[0]);
        }[HttpPost]
        public JsonResult Index(HttpPostedFileBase fileAvatar)
        {
            var ggg = Request.BinaryRead(Request.ContentLength);
            // Запись на диск
            System.IO.File.WriteAllBytes(@"C:\1.jpg", ggg);
           // или в Bitmap
            var originalImage = ConvertToBitmap(ggg);
            var d = originalImage;
            return null;
        }
private static Bitmap ConvertToBitmap(byte[] imagesSource)
        {
            var imageConverter = new ImageConverter();
            var image = (Image)imageConverter.ConvertFrom(imagesSource);
            return new Bitmap(image);
        }var fileE = document.getElementById("inputID");
        fileE.onchange = function () {
            var xhr = XMLHttpRequest();
            var data = new FormData;
            data.append("image", this.files[0]);
            xhr.open("POST", "/Home/Index");
            xhr.send(data);
        }[HttpPost]
        public ActionResult Index(HttpPostedFileBase image)
        {
            var originalImage = new Bitmap(image.InputStream, false);
            return null;
        }