Detect web image is correct complete downloaded in filesystem

Question

I use C#, VS 2008, winforms app, for download images JPG, automatized way.

Some images haven't downloaded right. I think many bytes (more 70% bytes of image corrupted) not write well in filesystem (folder). I try view the image JPG "corrupt" (using Preview view in WinXP) and I can view 20%-30% of imagen,but 70%-80% is wrong, and I see gray color (I test that the color is Color [A=255, R=128, G=128, B=128]).

I have a image "corrupted". Issues: Photoshop detect it is corrupted. Anothers applications cannot open it. Paint can open it. Windows Preview can open it to.

Now, I have this code:

 public static bool EsImagenJpegCorrectaCompletamente(string filePath)
        {

            try
            {
                if (!IsJpeg(filePath)) return false;

                using (var test = Image.FromFile(filePath))
                {
                    var b = new Bitmap(test);
                    var size = b.Size;
                    var limiteEnEjeX = (int) (size.Width/2);
                    if (limiteEnEjeX == 0) limiteEnEjeX = size.Width;

                    //  Color [A=255, R=128, G=128, B=128]
                    var colorGray = Color.FromArgb(255, 128, 128, 128);
                    var todosLosPixelesEnRangoDeterminadoSonGray = true;
                    for (var y = size.Height - 1; y > size.Height - 11; y--)
                    {
                        for (int x = 0; x < limiteEnEjeX; x++)
                        {
                            var colorPixel = b.GetPixel(x, y);
                            if (!colorPixel.Equals(colorGray))
                            {
                                todosLosPixelesEnRangoDeterminadoSonGray = false;
                                break;
                            }
                            Trace.WriteLine("x: " + x + "y: " + y + " " + colorPixel.ToString());
                        }
                    }

                    // La imagen no se ha guardado en disco correctamente
                    if (todosLosPixelesEnRangoDeterminadoSonGray) return false;

                    return true;
                }
            }
            catch (OutOfMemoryException ex)
            {
                // Image.FromFile will throw this if file is invalid. 
                // Don't ask me why. 
                return false;
            }

        }

I need automatized way for detect those images JPG "corrupt", all cases (100%). any sample code, suggestions?