Image img = Image.FromFile(name);
                List<PropertyItem> pis = img.PropertyItems.ToList<PropertyItem>();

Image imgnew = resizeImage(img,x[p],y[p]);// это функция такая самописная, которая меняет размер.
...

 foreach (PropertyItem pi in pis)
                    {
                        imgnew.SetPropertyItem(pi);
                    }

static void Main(string[] args)
        {

            {
                Bitmap image = new Bitmap(@"C:\inetpub\wwwroot\img\zhukov - копия\DSCN0298.JPG");
                UnicodeEncoding encoding = new UnicodeEncoding();

                foreach (PropertyItem propItem in image.PropertyItems)
                {
                    switch (propItem.Id)
                    {
                        case 0x013b: //315
                            Console.WriteLine("author: " + encoding.GetString(propItem.Value));
                            break;

                        case 0x9c9b:
                            Console.WriteLine("title: " + encoding.GetString(propItem.Value));
                            break;
                        case 0x9c9c:
                            Console.WriteLine("comments: " + encoding.GetString(propItem.Value));
                            break;
                        case 0x9c9d:
                            Console.WriteLine("author2: " + encoding.GetString(propItem.Value));
                            break;
                        case 0x9c9e:
                            Console.WriteLine("keywords: " + encoding.GetString(propItem.Value));
                            break;
                        case 0x9c9f:
                            Console.WriteLine("subject: " + encoding.GetString(propItem.Value));
                            break;
                    }
                }
                Console.ReadLine();

            }

PropertyItem propertyItem = propertyItemsResource.First<PropertyItem>(w => w.Id == 270);
propertyItem.Value = Encoding.UTF8.GetBytes(String.Format("{0}. Фото {1}\0", rusTextBox.Text, i + 1));
imgnew.SetPropertyItem(propertyItem);

int[] efix = new int[] { 315, 40091, 40092, 40094 };
foreach (int ef in efix)
                    {
                        propertyItem = propertyItemsResource.First<PropertyItem>(w => w.Id == ef);
                        imgnew.SetPropertyItem(propertyItem);
                    }