Concurrent Queue is getting full even after Dequeue. Is there problem in thread calls or anything else?

I am using ConcurrentQueue for multithreading operation. One thread is downloading Images from server and saving it to queue. Here is the code for that:

 public static void DownloadImage()
        {
            string baseUrl = "http://someurl";
            //int numIterations = 5;

            HttpWebRequest request = null;
            foreach (var fileName in fileNames)
            {
                    string url = string.Format(baseUrl, fileName);
                    request = (HttpWebRequest)WebRequest.Create(url);
                    request.Method = "GET";
                    request.ContentType = "application/x-www-form-urlencoded";
                    var response = (HttpWebResponse)request.GetResponse();
                    Stream stream = response.GetResponseStream();
                    img = Image.FromStream(stream);
                    ImageFileName FileNameImage = new ImageFileName(fileName, img);
                    ImageQueue.Enqueue(FileNameImage);
                    Console.WriteLine("Count after Enqueue: {0}", ImageQueue.Count);
             }

And another thread takes images from Queue and saves them on destination folder. Here is the code for that:

public static void SaveImage()
        {
            while (true)
            {
                if (!ImageQueue.IsEmpty)
                {
                    foreach (var newobject2 in ImageQueue)
                    {

                        Image img2 = newobject2.Image;
                        img2.Save("C:\\path" + newobject2.ImageName);
                        ZoomThumbnail = img2;
                        ZoomSmall = img2;
                        ZoomLarge = img2;

                        ZoomThumbnail = GenerateThumbnail(ZoomThumbnail, 86, false);
                        ZoomSmall = GenerateThumbnail(ZoomSmall, 400, false);
                        ZoomLarge = GenerateThumbnail(ZoomLarge, 1200, false);

                        ZoomThumbnail.Save("C:\\path" + newobject2.ImageName + "_Thumb.jpg");
                        ZoomSmall.Save("C:\\path" + newobject2.ImageName + "_ZoomSmall.jpg");
                        ZoomLarge.Save("C:\\path" + newobject2.ImageName + "_ZoomLarge.jpg");
                        ImageFileName imgobject3 = new ImageFileName();
                        ImageQueue.TryDequeue(out imgobject3);
                        Console.WriteLine("Count after Deque: {0}", ImageQueue.Count);

                    }


                }


            }

        }

I am calling these two threads from Button_Click() like this:

  Thread DownloadThread = new Thread(DownloadImage);
  DownloadThread.Start();
  Thread SaveThread = new Thread(SaveImage);
  SaveThread.Start();

I am getting MemoryFull error whenever queue reaches count of 68. I am not sure how I can avoid that. I have tried using Thread.Sleep before the start of second thread. But its not working. can anyone help?