gistfile1.cs

[HttpPost]
        public ActionResult Upload(HttpPostedFileBase file)
        {
            string fileName = System.IO.Path.GetFileName(file.FileName);
            string path = System.IO.Path.Combine(Server.MapPath("~/Images"), fileName );

            if (IMAGE_FILE_TYPES.Contains(Path.GetExtension(file.FileName).ToUpperInvariant()) && file.ContentLength <= MAX_FILE_SIZE)
            {
                file.SaveAs(path);
                string base64Image = Convert.ToBase64String(System.IO.File.ReadAllBytes(path));

                // From the shopify docs, this is the expected format
                // (http://api.shopify.com/asset.html#update)
                //{
                //  "asset": {
                //    "key": "assets/empty.gif",
                //    "attachment": "R0lGODlhAQABAPABAP///wAAACH5BAEKAAAALAAAAAABAAEAAAICRAEAOw==\n"
                //  }
                //}
                //so create the .NET equivalent of that
                dynamic assetData = new
                { 
                    asset = new { 
                        key = String.Format("assets/{0}", fileName),
                        attachment = base64Image
                    } 
                };

                var api = (ShopifyAPIClient)Session["API"];
                dynamic createBlogResponse = api.Put("/admin/themes/3175624/assets.json", assetData );

                // check response for valid call and delete image locally or put out error message if an error occurred

                System.IO.File.Delete(path);

                ViewBag.Message = "File uploaded successfully";
            }
            return View();
        }