void _cam_CaptureImageAvailable(object sender, ContentReadyEventArgs e)
        {
            string fileName = DateTime.Now.ToShortTimeString() + ".jpg";

            _library.SavePictureToCameraRoll(fileName, e.ImageStream);

            e.ImageStream.Seek(0, SeekOrigin.Begin);

            using (IsolatedStorageFile isStore = IsolatedStorageFile.GetUserStoreForApplication())
            {
                if (!isStore.FileExists(fileName))
                {
                    using (IsolatedStorageFileStream targetStream = isStore.OpenFile(fileName, FileMode.OpenOrCreate, FileAccess.Write))
                    {
                        byte[] readBuffer = new byte[4096];
                        int bytesRead = -1;

                        while ((bytesRead = e.ImageStream.Read(readBuffer, 0, readBuffer.Length)) > 0)
                        {
                            targetStream.Write(readBuffer, 0, bytesRead);
                        }
                    }
                }

            }
            e.ImageStream.Close();
        }