Where is the wrong in my code

I try to send an image to my sqlite database, and then to get back from the database to the appearance of an imageView. But during the execution of the program, i take no image to the image view and i get an error from Xamarin app output console . Where is the wrong in my code?

This is code, that i save image in database :

Bitmap bitmap = BitmapFactory.DecodeStream(stream);
                MemoryStream memStream = new MemoryStream();
                bitmap.Compress(Bitmap.CompressFormat.Png, 100, memStream);
                byte[] picData = memStream.ToArray();   

                _imgArt = Convert.ToBase64String(picData);                                  
            }

And this code, retrieve image to imageview :

 Bundle extras = Intent.Extras;     
                if (extras != null) {   
                    string image = sqldb_cursor.GetString (sqldb_cursor.GetColumnIndex ("Art"));             
                    byte[] photo = Convert.FromBase64String (image);
                    if (mArt != null)
                    {
                        var imageBitmap = BitmapFactory.DecodeByteArray(photo, 0, photo.Length);
                        RunOnUiThread(() => mArt.SetImageBitmap(imageBitmap));
                    }

And the error from Xamarin :

BitmapFactory﹕ Unable to decode stream: java.io.FileNotFoundException: