Convertir base64 d'Image en c#

Je suis en utilisant MVC#. Quand j'essaie De convertir en base64 de la chaîne de l'image, l'image n'est pas ouvert. Je suis en base64 de la chaîne à partir de javascript et coverting que pour l'image dans le contrôleur. Voici mon code.

var base64 = "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAABG4AAAH0CAYAAABsCGvoAAAgAElEQVR4Xuy9C5RV1Zmo++96P3ZVURSv4hEEFdQobYKtJESjJME+6WgTpPUQIrfpY8NRui/aKlcvY2hON0fN5TIUbh/6XDs9bgah0+1BY+gk2p2QFpIAgk9AiGBhlQgIokgVRQFVu3bd9S+c21WbXVV71157Pfb+loNh1ar5+Oc3Z/H46p9zRnqsR3ggAAEIQAACEIAABCAAAQhAAAIQgAAEAkcggrgJ3JwQEAQgAAEIQAACEIAABCAAAQhAAAIQsAkgblgIEIAABCAAAQhAAAIQgAAEIAABCEAgoAQQNwGdGMKCAAQgAAEIQAACEIAABCAAAQhAAAKIG9YABCAAAQhAAAIQgAAEIAABCEAAAhAIKAHETUAnhrAgAAEIQAACEIAABCAAAQhAAAIQgADihjUAAQhAAAIQgAAEIAABCEAAAhCAAAQCSgBxE9CJISwIQAACEIAABCAAAQhAAAIQgAAEIIC4YQ1AAAIQgAAEIAABCEAAAhCAAAQgAIGAEkDcBHRiCAsCEIAABCAAAQhAAAIQgAAEIAABCCBuWAMQgAAEIAABCEAAAhCAAAQgAAEIQCCgBBA3AZ0YwoIABCAAAQhAAAIQgAAEIAABCEAAAogb1gAEIAABCEAAAhCAAAQgAAEIQAACEAgoAcRNQCeGsCAAAQhAAAIQgAAEIAABCEAAAhCAAOKGNQABCEAAAhCAAAQgAAEIQAACEIAABAJKAHET0IkhLAhAAAIQgAAEIAABCEAAAhCAAAQggLhhDUAAAhCAAAQgAAEIQAACEIAABCAAgYASQNwEdGIICwIQgAAEIAABCEAAAhCAAAQgAAEIIG5YAxCAAAQgAAEIQAACEIAABCAAAQhAIKAEEDcBnRjCggAEIAABCEAAAhCAAAQgAAEIQAACiBvWAAQgAAEIQAACEIAABCAAA...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";

byte[] str = System.Text.Encoding.Unicode.GetBytes(base64);
var buffer = Convert.FromBase64String(Convert.ToBase64String(str));
var file = Server.MapPath("~/Content/images/err.png");
System.IO.File.WriteAllBytes(file, buffer);
Image img = new Image();
img.ImageUrl = Server.MapPath("~/Content/images/err.png");