Thumnail image is returned via handler. First time all is OK. but when I do refresh, then istead of image is displayd some machine code in Firefox.

I traced to root cause with Fiddler, it is because first time Content-Type comes correctly image/png

but with refresh it is coming as text/html. what should be added, that after refresh browser still could get image/png? below is my code

Bitmap target = new Bitmap(width, height);
                    context.Response.ContentType = "image/png";
                    

                    using (Graphics graphics = Graphics.FromImage(target))
                    {
                        graphics.CompositingQuality = CompositingQuality.HighSpeed;
                        graphics.InterpolationMode = InterpolationMode.HighQualityBicubic;
                        graphics.CompositingMode = CompositingMode.SourceCopy;
                        graphics.DrawImage(photo, 0, 0, width, height);


                        HttpCachePolicy cachePolicy = context.Response.Cache;
                        cachePolicy.SetCacheability(HttpCacheability.Public);
                        cachePolicy.VaryByParams["car_image_id"] = true;
                        cachePolicy.SetOmitVaryStar(true);
                        cachePolicy.SetExpires(DateTime.Now + TimeSpan.FromDays(365));
                        cachePolicy.SetValidUntilExpires(true);

                        using (MemoryStream memoryStream = new MemoryStream())
                        {
                            target.Save(memoryStream, ImageFormat.Png);
                            //cashing

                            using (FileStream diskCacheStream = new FileStream(cachePath, FileMode.CreateNew))
                            {
                                memoryStream.WriteTo(diskCacheStream);
                            }
                            memoryStream.WriteTo(context.Response.OutputStream);
                        }
                        context.Response.End();
                        target.Dispose();