文件签名一般都在文件的头部，如果你用十六进制方式查看文件，你就可以看到文件的一些签名信息。如用uestudio以十六进制方式查看zip格式的文件，其文件内容头部有50 4B 03 04这样的十六进制信息。同理jpg文件状况有FF D8 FF E0 xx xx 4A 46这样的十六进制信息，其实这此十六进制都是表示一些特殊字条。

php怎么样验证文件类型？先来看一个简单的方法：

	function checkFileType($fileName){          $file = fopen($fileName, "rb");          $bin = fread($file, 2); //只读2字节          fclose($file);  老品牌娱乐城		// C为无符号整数，网上搜到的都是c，为有符号整数，这样会产生负数判断不正常         $strInfo  = @unpack("C2chars", $bin);         $typeCode = intval($strInfo[‘chars1‘].$strInfo[‘chars2‘]);          $fileType = ‘‘;  		switch( $typeCode )		{			case ‘255216‘:				return $typeCode. ‘ : ‘ .‘jpg‘;				break;			case ‘7173‘:				return $typeCode. ‘ : ‘ .‘gif‘;				break;			case ‘13780‘:				return $typeCode. ‘ : ‘ .‘png‘;				break;			case ‘6677‘:				return $typeCode. ‘ : ‘ .‘bmp‘;				break;			case ‘7790‘:				return $typeCode. ‘ : ‘ .‘exe‘;				break;			case ‘7784‘:				return $typeCode. ‘ : ‘ .‘midi‘;				break;			case ‘8297‘:				return $typeCode. ‘ : ‘ .‘rar‘;				break;			default:				return $typeCode. ‘ : ‘ .‘Unknown‘;				break;		}		//return $typeCode;    }		$file_name = ‘11.doc‘;	echo checkFileType($file_name);

下来提供一个类的实现：

/*通过文件名，获得文件类型* *@author chengmo QQ:8292669* *@copyright http://www.cnblogs.com/chengmo 2010-10-17 *@version 0.1 *$filename="d:/1.png";echo cFileTypeCheck::getFileType($filename); 打印：png */class cFileTypeCheck{    private static $_TypeList=array();    private static $CheckClass=null;    private function __construct($filename)    {        self::$_TypeList=$this->getTypeList();    }     /**     *处理文件类型映射关系表*     *     * @param string $filename 文件类型     * @return string 文件类型，没有找到返回：other     */    private function _getFileType($filename)    {        $filetype="other";        if(!file_exists($filename)) throw new Exception("no found file!");        $file = @fopen($filename,"rb");        if(!$file) throw new Exception("file refuse!");        $bin = fread($file, 15); //只读15字节 各个不同文件类型，头信息不一样。        fclose($file);                 $typelist=self::$_TypeList;        foreach ($typelist as $v)        {            $blen=strlen(pack("H*",$v[0])); //得到文件头标记字节数            $tbin=substr($bin,0,intval($blen)); ///需要比较文件头长度                         if(strtolower($v[0])==strtolower(array_shift(unpack("H*",$tbin))))             {                return $v[1];            }        }        return $filetype;    }         /**     *得到文件头与文件类型映射表*     *     * @return array array(array(‘key‘,value)...)     */    public function getTypeList()    {        return array(array("FFD8FFE1","jpg"),        array("89504E47","png"),        array("47494638","gif"),        array("49492A00","tif"),        array("424D","bmp"),        array("41433130","dwg"),        array("38425053","psd"),        array("7B5C727466","rtf"),        array("3C3F786D6C","xml"),        array("68746D6C3E","html"),        array("44656C69766572792D646174","eml"),        array("CFAD12FEC5FD746F","dbx"),        array("2142444E","pst"),        array("D0CF11E0","xls/doc"),        array("5374616E64617264204A","mdb"),        array("FF575043","wpd"),        array("252150532D41646F6265","eps/ps"),        array("255044462D312E","pdf"),        array("E3828596","pwl"),        array("504B0304","zip"),        array("52617221","rar"),        array("57415645","wav"),        array("41564920","avi"),        array("2E7261FD","ram"),        array("2E524D46","rm"),        array("000001BA","mpg"),        array("000001B3","mpg"),        array("6D6F6F76","mov"),        array("3026B2758E66CF11","asf"),        array("4D546864","mid"));    }  	    public static function getFileType($filename)    {        if(!self::$CheckClass) self::$CheckClass=new self($filename);        $class=self::$CheckClass;        return $class->_getFileType($filename);    }	}$filename="22.jpg";echo $filename,"t",cFileTypeCheck::getFileType($filename),"rn";$filename="11.doc";echo $filename,"t",cFileTypeCheck::getFileType($filename),"rn";

或者可以这么检测：

$filename = ‘22.jpg‘; $extname = strtolower(substr($filename, strrpos($filename, ‘.‘) + 1));echo $extname.‘<br />‘;$file = @fopen($filename, ‘rb‘);    if ($file)    {        $str = @fread($file, 0x400); // 读取前 1024 个字节		echo substr($str, 0, 4);        @fclose($file);    } 	if (substr($str, 0, 4) == ‘MThd‘ && $extname != ‘txt‘)        {            $format = ‘mid‘;        }        elseif (substr($str, 0, 4) == ‘RIFF‘ && $extname == ‘wav‘)        {            $format = ‘wav‘;        }        elseif (substr($str ,0, 3) == "/xFF/xD8/xFF")        {            $format = ‘jpg‘;        }        elseif (substr($str ,0, 4) == ‘GIF8‘ && $extname != ‘txt‘)        {            $format = ‘gif‘;        }        elseif (substr($str ,0, 8 ) == "/x89/x50/x4E/x47/x0D/x0A/x1A/x0A")        {            $format = ‘png‘;        }        elseif (substr($str ,0, 2) == ‘BM‘ && $extname != ‘txt‘)        {            $format = ‘bmp‘;        }        elseif ((substr($str ,0, 3) == ‘CWS‘ || substr($str ,0, 3) == ‘FWS‘) && $extname != ‘txt‘)        {            $format = ‘swf‘;        }        elseif (substr($str ,0, 4) == "/xD0/xCF/x11/xE0")        {   // D0CF11E == DOCFILE == Microsoft Office Document            if (substr($str,0x200,4) == "/xEC/xA5/xC1/x00" || $extname == ‘doc‘)            {                $format = ‘doc‘;            }            elseif (substr($str,0x200,2) == "/x09/x08" || $extname == ‘xls‘)            {                $format = ‘xls‘;            } elseif (substr($str,0x200,4) == "/xFD/xFF/xFF/xFF" || $extname == ‘ppt‘)            {                $format = ‘ppt‘;            }        } elseif (substr($str ,0, 4) == "PK/x03/x04")        {            $format = ‘zip‘;        } elseif (substr($str ,0, 4) == ‘Rar!‘ && $extname != ‘txt‘)        {            $format = ‘rar‘;        } elseif (substr($str ,0, 4) == "/x25PDF")        {            $format = ‘pdf‘;        } elseif (substr($str ,0, 3) == "/x30/x82/x0A")        {            $format = ‘cert‘;        } elseif (substr($str ,0, 4) == ‘ITSF‘ && $extname != ‘txt‘)        {            $format = ‘chm‘;        } elseif (substr($str ,0, 4) == "/x2ERMF")        {            $format = ‘rm‘;        } elseif ($extname == ‘sql‘)        {            $format = ‘sql‘;        } elseif ($extname == ‘txt‘)        {            $format = ‘txt‘;        }				echo $format;

根据文件头检测文件类型