php - Reading a File's Metadata

Question

I am making a gallery implementation for PHP.

The administrator is able to access the upload page, where he would upload and categorize the image. So far so good.

The implementation will allow users to comment on the pictures the admin has uploaded, so I'm implementing a database table to link comments with their respective images.

id | path .:. id | datetime | comment_title | comment_body | uid

So far so good.

I want the administrator to have the ability to rename files (not necessarily via the site, but via FTP or otherwise root access), and not break the whole system.

So I was thinking of implementing a metadata system to link the ID with the image. That would save me both the first table, and will allow free manipulation of the image (both move it inside folders, rename it, etc).

The question is, how do I implement it? How do I write a metadata attached to a file, and how do I read it? Google gave no real results on this one.

If there's a better way of doing it, I'd love to hear as well!

Will appreciate any help!

Answer 1

While I have not used this myself the XMP PHP Toolkit on sourceforge sounds like just what you might be looking for: http://xmpphptoolkit.sourceforge.net/ That being said - it's in alpha and hasn't been updated in over a year it appears.

XMP Toolkit PHP Extension is a PHP module which includes the Adobe XMP Toolkit SDK. This PHP5 extension will provide classes and methods to manipulate XMP Metadatas from files like jpegs, tiff, png, but also wav, mp3, avi, mpeg4, pdf, ai, eps… It’s based from the Adobe XMP Toolkit SDK 4.4.2. The goal of this extension is to have php classes which can open files, extract metadatas, manipulate them, and put them back within few lines of php code. This project is under GPL v3 License.

You are also be able to write arbitrary metadata to an image file with iptcembed. As you mention in your comment this only works for JPEG files.

http://php.net/manual/en/function.iptcembed.php

Here is a script from the comments of a class that will get and set IPTC data:

<?

    /************************************************************

        IPTC EASY 1.0 - IPTC data manipulator for JPEG images

        All reserved www.image-host-script.com

        Sep 15, 2008

    ************************************************************/

    DEFINE('IPTC_OBJECT_NAME', '005');
    DEFINE('IPTC_EDIT_STATUS', '007');
    DEFINE('IPTC_PRIORITY', '010');
    DEFINE('IPTC_CATEGORY', '015');
    DEFINE('IPTC_SUPPLEMENTAL_CATEGORY', '020');
    DEFINE('IPTC_FIXTURE_IDENTIFIER', '022');
    DEFINE('IPTC_KEYWORDS', '025');
    DEFINE('IPTC_RELEASE_DATE', '030');
    DEFINE('IPTC_RELEASE_TIME', '035');
    DEFINE('IPTC_SPECIAL_INSTRUCTIONS', '040');
    DEFINE('IPTC_REFERENCE_SERVICE', '045');
    DEFINE('IPTC_REFERENCE_DATE', '047');
    DEFINE('IPTC_REFERENCE_NUMBER', '050');
    DEFINE('IPTC_CREATED_DATE', '055');
    DEFINE('IPTC_CREATED_TIME', '060');
    DEFINE('IPTC_ORIGINATING_PROGRAM', '065');
    DEFINE('IPTC_PROGRAM_VERSION', '070');
    DEFINE('IPTC_OBJECT_CYCLE', '075');
    DEFINE('IPTC_BYLINE', '080');
    DEFINE('IPTC_BYLINE_TITLE', '085');
    DEFINE('IPTC_CITY', '090');
    DEFINE('IPTC_PROVINCE_STATE', '095');
    DEFINE('IPTC_COUNTRY_CODE', '100');
    DEFINE('IPTC_COUNTRY', '101');
    DEFINE('IPTC_ORIGINAL_TRANSMISSION_REFERENCE',     '103');
    DEFINE('IPTC_HEADLINE', '105');
    DEFINE('IPTC_CREDIT', '110');
    DEFINE('IPTC_SOURCE', '115');
    DEFINE('IPTC_COPYRIGHT_STRING', '116');
    DEFINE('IPTC_CAPTION', '120');
    DEFINE('IPTC_LOCAL_CAPTION', '121');

    class iptc {
        var $meta=Array();
        var $hasmeta=false;
        var $file=false;


        function iptc($filename) {
            $size = getimagesize($filename,$info);
            $this->hasmeta = isset($info["APP13"]);
            if($this->hasmeta)
                $this->meta = iptcparse ($info["APP13"]);
            $this->file = $filename;
        }
        function set($tag, $data) {
            $this->meta ["2#$tag"]= Array( $data );
            $this->hasmeta=true;
        }
        function get($tag) {
            return isset($this->meta["2#$tag"]) ? $this->meta["2#$tag"][0] : false;
        }

        function dump() {
            print_r($this->meta);
        }
        function binary() {
            $iptc_new = '';
            foreach (array_keys($this->meta) as $s) {
                $tag = str_replace("2#", "", $s);
                $iptc_new .= $this->iptc_maketag(2, $tag, $this->meta[$s][0]);
            }        
            return $iptc_new;    
        }
        function iptc_maketag($rec,$dat,$val) {
            $len = strlen($val);
            if ($len < 0x8000) {
                   return chr(0x1c).chr($rec).chr($dat).
                   chr($len >> 8).
                   chr($len & 0xff).
                   $val;
            } else {
                   return chr(0x1c).chr($rec).chr($dat).
                   chr(0x80).chr(0x04).
                   chr(($len >> 24) & 0xff).
                   chr(($len >> 16) & 0xff).
                   chr(($len >> 8 ) & 0xff).
                   chr(($len ) & 0xff).
                   $val;

            }
        }    
        function write() {
            if(!function_exists('iptcembed')) return false;
            $mode = 0;
            $content = iptcembed($this->binary(), $this->file, $mode);    
            $filename = $this->file;

            @unlink($filename); #delete if exists

            $fp = fopen($filename, "w");
            fwrite($fp, $content);
            fclose($fp);
        }    

        #requires GD library installed
        function removeAllTags() {
            $this->hasmeta=false;
            $this->meta=Array();
            $img = imagecreatefromstring(implode(file($this->file)));
            @unlink($this->file); #delete if exists
            imagejpeg($img,$this->file,100);
        }
    };


?>

Example read copyright string:

$i = new iptc("test.jpg");
echo $i->get(IPTC_COPYRIGHT_STRING); 

Update copyright statement:

$i = new iptc("test.jpg");
echo $i->set(IPTC_COPYRIGHT_STRING,"Here goes the new data"); 
$i->write();