How to determine image type by getting header information in PHP_PHP Tutorial

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$filename = '617.gif' ;

function pictype ( $file )

{

/*$png_header = "/x89/x50/x4e/x47/x0d/x0a/x1a/x0a";

$jpg_header = "/xff/xd8";*/

$header = file_get_contents ( $file , 0 , NULL , 0 , 5 );

//echo bin2hex($header);

if ( $header { 0 }. $header { 1 }== "/x89/x50" )

{

return 'png' ;

}

else if( $header { 0 }. $header { 1 } == "/xff/xd8" )

{

return 'jpeg' ;

}

else if( $header { 0 }. $header { 1 }. $header { 2 } == "/x47/x49/x46" )

{

if( $header { 4 } == "/x37" )

return 'gif87' ;

else if( $header { 4 } == "/x39" )

return 'gif89' ;

}

}

echo pictype ( $filename );