<?php

    /*
        JPEG Validator

        Aktion: PHP Scripte für die armen dieser Welt
        Der Erlös geht für mein Pausenbrot drauf 

        Copyright (c) 2004 by Phillip 'Firebird' Berndt
    */
    
    function chrToVal($text)
    {
        $hexCode = '';
        for($i=0;$i<strlen($text);$i++)
            $hexCode .= dechex(ord($text[$i]));
        return hexdec($hexCode);
    }
    
    function validateJpeg($text)
    {
        $jpgLen = chrToVal(substr($text, 0, 2));
        
        $jpgIdentify = substr($text, 5, 5);
            if(ord($jpgIdentify[0]) != 0x10 || substr($jpgIdentify, 1) != 'JFIF')
                return false;
                
        $jpgVersion = substr($text, 11, 2);
        $jpgVersion = chrToVal($jpgVersion[0]).'.'.chrToVal($jpgVersion[1]);
            if($jpgVersion != '1.2') 
                return false;
                
        $pixelFormat = chrToVal(substr($text, 13, 1));
        $xDensity = chrToVal(substr($text, 14, 2));
        $yDensity = chrToVal(substr($text, 16, 2));
        
        if($xDensity != $yDensity) return false;
        
        $xThumb = chrToVal(substr($text, 18, 1));
        $yThumb = chrToVal(substr($text, 19, 1));
        
        if(($xThumb == 0 && $yThumb != 0) || ($xThumb != 0 && $yThumb == 0))
            return false;
            
        return true;
    }
    
    $jpegContent = implode('', file('Beispiel.jpg'));
    $isValid = validateJpeg($jpegContent) ? 'valid' : 'invalid';
    
    echo('This picture is '.$isValid);
?>