$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 );