Diff two file per byte. Read file and represent as HEX string. Read Hex string, convert to byte and write to file.

gistfile1.cs

        public static void DiffPerByte(string path1, string path2)
        {
            byte[] file1 = System.IO.File.ReadAllBytes(path1);
            byte[] file2 = File.ReadAllBytes(path2);
            Console.WriteLine("{0} len: {1}", path1, file1.Length);
            Console.WriteLine("{0} len: {1}", path2, file2.Length);

            int len = file2.Length < file1.Length ? file2.Length : file1.Length;
            for (int i = 0; i < len; i++)
            {
                if (file1[i] != file2[i])
                {
                    Console.WriteLine("They are diffrence since index: {0}", i);
                    return;
                }
            }

            Console.WriteLine("same");
        }

        public static string jpgToByteString(string jpgPath)
        {
            if (string.IsNullOrEmpty(jpgPath))
            {
                throw new ArgumentNullException("jpgPath");
            }

            byte[] bytes = System.IO.File.ReadAllBytes(jpgPath);
            string ret = string.Empty;
            for (int i = 0; i < bytes.Length; i++)
            {
                ret = string.Concat(ret, bytes[i].ToString("X2")); // 00~FF
            }

            return ret;
        }

        public static void byteStringToJpg(string hexStringFilePath, string jpgPath)
        {
            if (string.IsNullOrEmpty(jpgPath))
            {
                throw new ArgumentNullException("jpgPath");
            }

            if (string.IsNullOrEmpty(hexStringFilePath))
            {
                throw new ArgumentNullException("hexStringFilePath");
            }

            if (File.Exists(jpgPath))
            {
                File.Delete(jpgPath);
            }

            if (!File.Exists(hexStringFilePath))
            {
                throw new FileNotFoundException(hexStringFilePath + " not found");
            }

            char[] buff = new char[2]; // 00~FF

            using (FileStream fstream = new FileStream(hexStringFilePath, FileMode.Open))
            using(StreamReader reader = new StreamReader(fstream))
            using(FileStream jpgStream =  new FileStream(jpgPath, FileMode.CreateNew, FileAccess.Write))
            {
                int index = 0;
                int count = 0;
                do
                {
                    count = reader.Read(buff, 0, buff.Length);

                    if (count <= 0)
                    {
                        break; // read complete
                    }

                    byte b = 0;
                    if (count > 1)
                    {
                        b = byte.Parse(string.Concat<char>(buff), System.Globalization.NumberStyles.HexNumber);
                    }
                    else
                    {
                        b = byte.Parse(buff[0].ToString(), System.Globalization.NumberStyles.HexNumber);
                    }

                    jpgStream.WriteByte(b);

                    index += count;
                } while (count > 0 && !reader.EndOfStream);
            }
        }