检核图片文件类型

　　　　　/// <summary>
        /// 检核文件类型
        /// </summary>
        /// <param name="strFileName"></param>
        /// <returns></returns>
        public string getFileType(string strFileName)
        {
            try
            {
                Dictionary<string, string> dicFileType = new Dictionary<string, string>();
                dicFileType.Add("255216", "JPG");
                dicFileType.Add("6677", "BMP");
                dicFileType.Add("13780", "PNG");
                dicFileType.Add("3780", "PDF");
                dicFileType.Add("12392", "RTF");

                System.IO.FileStream fs = new System.IO.FileStream(strFileName, System.IO.FileMode.Open, System.IO.FileAccess.Read);
                System.IO.BinaryReader reader = new System.IO.BinaryReader(fs);
                string fileClass;
                byte buffer;
                byte[] b = new byte[2];
                buffer = reader.ReadByte();
                b[0] = buffer;
                fileClass = buffer.ToString();
                buffer = reader.ReadByte();
                b[1] = buffer;
                fileClass += buffer.ToString();


                reader.Close();
                fs.Close();

                return dicFileType[fileClass];
            }
            catch (Exception ex)
            {
                throw ex;
            }
        }