This file, written in PHP 4, parsed qmail messages piped to it via a procmail rule (if I remember correctly). The script will parse anything sent to it via stdin.

qmail_popper.php

<?php
/**
* @note Qmail popper::PHP4::qmail-popper-php
* @author Stefan Antonowicz
*
* This file parses out the mails sent to qmail via stdin.
*
* @author Stefan Antonowicz
*/

error_reporting(E_ERROR | E_WARNING | E_PARSE);

/* Set constants and variables */

$mime_types = array( 'image/jpeg'=>'.jpg', 'image/jpg'=>'.jpg', 'image/gif'=>'.gif', 'image/png'=>'.png' );
$x_scale = 189;
define( 'ATTACH_DEST', '/home/foo/bar' );
define( 'ATTACH_TMP', '/tmp' );

/*
* A file name can be passed in instead i.e. `which php` qmail_popper.php -f foo.txt
*/

if( $argv[1] == '-f' ) {
    $fp = fopen( $argv[2], 'r' );
} else {
    $fp = fopen( "php://stdin", "r" );
}

if(! $fp ) exit( 0 ); 

$mail = '';
while(! feof( $fp ) ) {
    $line = fread( $fp, 1024 );
    $mail .= $line;
}

fclose( $fp );

/* 
* Time to start parsing out the headers, body, and attachments.  Some of this
*  borrowed from the PEAR mimeDecode class.  
*/
    
$mail  = preg_replace( "/\r?\n/", "\r\n", $mail );
$mail  = preg_replace( "/\r\n(\t| )+/", ' ', $mail );
$mail_array = explode( "\r\n", trim( $mail ) );

foreach( $mail_array as $elem ) {
    $elem = trim( $elem );
    $name = substr( $elem, 0, $pos = strpos( $elem, ':' ) );
    $value = substr( $elem, $pos + 1 );
        
    /* These are because PHP4 doesn't have stripos */
    $lower_name = strtolower( $name );
    $lower_elem = strtolower( $elem );
    $lower_value = strtolower( $value );
        
    /* Catch FROM and TO addresses in <foo@example.org> format */
     if( preg_match( "/<(.*)>/sU", $value, $match ) ) $value = $match[1];
     $value = trim( $value );
     
     if( $name ) {
        if( strpos( $lower_name, 'content-type' ) !== FALSE ) {
            /* get attachment type and set it as key.  Also see if header is in the "forbidden" list */
            preg_match( '/(.*)($|;)/sU', $value, $key );
            preg_match( '/;.*=(.*)$/sU', $value, $mime_name );
                
            /* some systems put quotes around the mime name, others don't */
            if( $mime_name[1] ) $mime_name = str_replace( '"', '', $mime_name[1] );    
            if( in_array( $mime_name, $bad_attach ) ) continue;            
            
            $headers[$name][] = $value;
            $curname = trim( $key[1] );
        } else {
            $headers[$name] = $value;
        }
    } elseif( $elem && strpos( $lower_elem, '_part_' ) === FALSE && strpos( $lower_elem, 'dngr' ) == FALSE ) {
        $body[$curname][] = $elem;
    }
}

$msg_array = $body['text/plain'] ? $body['text/plain'] : strip_tags( $body['text/html'] );

/*
*  NOTE: I submitted the message to the database and got a unique id for it, identified
*  as $msgid.  I also tried to determine the user information and parse any
*  messages the user sent via SMS, which aren't important for this demonstration
*/

if(! $msgid ) exit( 0 );
$image_file = "img_" . time( ) . "_" . $msgid;


/*
*       IMAGE HANDLING
*/

foreach( $mime_types as $type=>$ext ) {
    if( array_key_exists( $type, $body ) ) {
        $image_file .= $ext;
        $attach = implode( "\n", $body[$type] );
        $check_type = $type;
    }
}

if( ! $attach ) exit( 0 );

$payload        = ATTACH_TMP. $image_file;       
$h = fopen( $payload, 'w' );
fwrite( $h, base64_decode( $attach ) );
fclose( $h );
    
if( class_exists( 'finfo' ) ) {
    $finfo = new finfo( FILEINFO_MIME, MIME_DB ); // return mime type ala mimetype extension
    $mtype = $finfo->file( $payload );
} else {
    $mtype = trim( exec( 'file -bi ' . escapeshellarg( $payload ) ) );
}
        
if( $mtype != $check_type ) {
    unlink( $payload ); 
    exit( 0 );      
}
    
/*
 * Here I would pull the name of the last image submitted by the user, which would be $last_image
*/
    
    
$last_image = $game->lastImage( );
if(! $last_image || md5( file_get_contents( $payload ) ) != md5( file_get_contents( $last_image ) ) )  {
    unlink( $payload );
    exit( 0 );
}
    
/*  
* Looking good - make directories and move the file over.  This requires a user id generated earlier
*/
$dest_dir       = ATTACH_DEST . $user->id;
$thumb_dir      = ATTACH_DEST . $user->id . '/thumbs';
$destination    = $dest_dir . '/' . $image_file;

if(! is_dir( $dest_dir ) ) 
   @mkdir( $dest_dir, 0777 );
   
if(! is_dir( $thumb_dir ) )
   @mkdir( $thumb_dir, 0777 );
    
rename( $payload, $destination );
exit( 0 );
?>