判断图片byte[]是否合法

代码

bool IsValidPic(byte[] bts)
        {
if (bts == null || bts.Length < 4)
            {
return false;
            }
string fileClass = "";
int len = bts.Length;
try
            {
                fileClass = bts[0].ToString();
                fileClass += bts[1].ToString();
                fileClass = fileClass.Trim();
if (fileClass == "7173" || fileClass == "13780")//7173是gif;,13780是PNG;
                {
return true;
                }
else      // JpgOrJpeg
                {
byte[] Jpg = new byte[4];

                    Jpg[0] = 0xff;

                    Jpg[1] = 0xd8;

                    Jpg[2] = 0xff;

                    Jpg[3] = 0xd9;

if (bts[0] == Jpg[0] && bts[1] == Jpg[1]
&& bts[len - 2] == Jpg[2] && bts[len - 1] == Jpg[3])
                    {
return true;
                    }
else
                    {
return false;
                    }
                }
            }
catch (Exception ex)
            {
//Log.WriteLog(e.ToString() + "  fileclass = " + fileClass);
                WriteLog.LogException(ex);
return false;
            }
        }