Problema con script thumb.php v1.1

Salve io ho usato lo script trovato qui

http://mightystuff.net/php_thumbnail_script

che vi riporto per completezza

<?php
/* 
    thumb.php v1.1
    ______________________________________________________________________ 
    Creates a thumbnailed image based on info passed to it via $_GET. 
    
    Images are cached on the server, so server processing overhead is only 
    needed for the first time the script runs on a particular image.
    ______________________________________________________________________
    Requires:
        GD Library
    ______________________________________________________________________
    Copyright: 
        (C) 2003 Chris Tomlinson. christo@mightystuff.net
        http://mightystuff.net
        
        This library is free software; you can redistribute it and/or
        modify it under the terms of the GNU Lesser General Public
        License as published by the Free Software Foundation; either
        version 2.1 of the License, or (at your option) any later version.
        
        This library is distributed in the hope that it will be useful,
        but WITHOUT ANY WARRANTY; without even the implied warranty of
        MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
        Lesser General Public License for more details.
    
        http://www.gnu.org/copyleft/lesser.txt
    ______________________________________________________________________
    Configuration:
        set $thumb_size to be a default maximum width/height if not passed via get
        set $image_error to be an image to be used when there is a problem parsing the image
        set $site_config['path_thumbnail'] to be a write-permissable folder on your server relative to the DOCUMENT_ROOT for storing images so they cache on the server.
        set $quality to be a value 0-100 for the resulting thumbnail jpeg quality
    ______________________________________________________________________    
    Usage:
        <img src="thumb.php?file=FILE&size=SIZE">
        
        Where:
        FILE    =    the file to retrieve
        SIZE    =    the maximum size of the thumbnail in pixels
    ______________________________________________________________________
    Changes:
        0.1 - first release
        0.2 - converted cache thumbnail from png to jpeg
        0.3 - fixed error where files weren't being cached properly
        0.4 - allowed non local urls (if allow_url_fopen is on), quality and nocache switches
        0.5 - allowed maximum x and y settings (for scaling images to fit non square sizes)
        0.6 - allowed tagging of images (with the get query placing the text in the bottom left hand corner of the image)
        0.7 - fixed gd_info error for php<4.3
        0.8 - added gif support (for gd 2.0.28)
        0.9 - now supports native outputting of png, jpg and gif formats
        1.0 - doesn't fail if the cache file can't be created
        1.1 - removed a few more notices
*/
//script configuration
ini_set('memory_limit','64M');
$site_config['document_root'] = $_SERVER['DOCUMENT_ROOT'];
$thumb_size = 128; //all thumbnails are this maximum width or height if not specified via get
$site_config['absolute_uri']=str_replace('///','//',str_replace('thumb.php?'.$_SERVER['QUERY_STRING'],'',$_SERVER['REQUEST_URI']));
$site_config['path_thumbnail']=$site_config['absolute_uri'].'/cache/images/';    //where to cache thumbnails on the server, relative to the DOCUMENT_ROOT
$image_error=$site_config['document_root'].$site_config['absolute_uri'].'/images/icons/image_error.png';    // used if no image could be found, or a gif image is specified

$thumb_size_x = 0;
$thumb_size_y = 0;

# Define quality of image
if (@$_GET["quality"]<>0) {
    $quality    = $_GET["quality"];
} else {
    $quality    = 80;
}

# Define size of image (maximum width or height)- if specified via get.
if (@$_GET["size"]<>0) {
    $thumb_size=intval($_GET["size"]);
}
if (intval(@$_GET["sizex"])>0)
{
    $thumb_size_x=intval($_GET["sizex"]);
    if (intval(@$_GET["sizey"])>0) 
    {
        $thumb_size_y=intval($_GET["sizey"]);
    } else {
        $thumb_size_y=$thumb_size_x;
    }
}

if (file_exists($_GET['file']))
{
    $filename=$_GET['file'];
} else {
    $filename=str_replace('//','/',$site_config['document_root'].$site_config['absolute_uri'].'/'.$_GET["file"]);
}

# If calling an external image, remove document_root
if (substr_count($filename, "http://")>0)

{
    $filename=str_replace($site_config['document_root'].$site_config['absolute_uri'].'/','',$filename);
}

$filename=str_replace("\'","'",$filename);
$filename=rtrim($filename);
$filename=str_replace("//","/",$filename);
$fileextension=substr($filename, strrpos ($filename, ".") + 1);

$cache_file=str_replace('//','/',$site_config['document_root'].$site_config['path_thumbnail'].md5($filename.@$thumb_size.@$thumb_size_x.@$thumb_size_y.@$quality).'.'.$fileextension);

# remove cache thumbnail?
if (@$_GET['nocache']==1)
{
    if (file_exists($cache_file))
    {
        #remove the cached thumbnail
        unlink($cache_file);
    }
}

if ((file_exists($cache_file)) && (@filemtime($cache_file)>@filemtime($filename)))
{
    header('Content-type: image/'.$fileextension);
    header("Expires: Mon, 26 Jul 2030 05:00:00 GMT");    
    header('Content-Disposition: inline; filename='.str_replace('/','',md5($filename.$thumb_size.$thumb_size_x.$thumb_size_y.$quality).'.'.$fileextension));
    echo (join('', file( $cache_file )));
    exit; # no need to create thumbnail - it already exists in the cache
}

# determine php and gd versions
$ver=intval(str_replace(".","",phpversion()));
if ($ver>=430)
{
    $gd_version=@gd_info();
}

# define the right function for the right image types
if (!$image_type_arr = @getimagesize($filename))
{
    header('Content-type: image/png');
    if(@$_GET['noerror'])
    {
        exit;
    } else {    
        echo (join('', file( $site_config['document_root'].$image_error )));
        exit;
    }
} 
$image_type=$image_type_arr[2];

switch ($image_type)
{
    case 2: # JPG
        if (!$image = @imagecreatefromjpeg ($filename))
        {
            # not a valid jpeg file
            $image = imagecreatefrompng ($image_error);
            $file_type="png";
            if (file_exists($cache_file))
            {
                # remove the cached thumbnail
                unlink($cache_file);
            }
        } 
        break;

    case 3: # PNG
        if (!$image = @imagecreatefrompng ($filename))
        {
            # not a valid png file
            $image = imagecreatefrompng ($image_error);
            $file_type="png";            
            if (file_exists($cache_file))
            {
                # remove the cached thumbnail
                unlink($cache_file);
            }
        }             
        break;

    case 1: # GIF 
        if (!$image = @imagecreatefromgif ($filename))
        {
            # not a valid gif file
            $image = imagecreatefrompng ($image_error);
            $file_type="png";            
            if (file_exists($cache_file))
            {
                # remove the cached thumbnail
                unlink($cache_file);
            }
        }             
        break;
    default:
        $image = imagecreatefrompng($image_error); 
        break;

}

# define size of original image    
$image_width = imagesx($image);
$image_height = imagesy($image);

# define size of the thumbnail    
if (@$thumb_size_x>0)
{
    # define images x AND y
    $thumb_width = $thumb_size_x;
    $factor = $image_width/$thumb_size_x;
    $thumb_height = intval($image_height / $factor); 
    if ($thumb_height>$thumb_size_y)
    {
        $thumb_height = $thumb_size_y; 
        $factor = $image_height/$thumb_size_y;
        $thumb_width = intval($image_width / $factor); 
    }        
} else {
    # define images x OR y
    $thumb_width = $thumb_size; 
    $factor = $image_width/$thumb_size;
    $thumb_height = intval($image_height / $factor); 
    if ($thumb_height>$thumb_size)
    {
        $thumb_height = $thumb_size; 
        $factor = $image_height/$thumb_size;
        $thumb_width = intval($image_width / $factor); 
    }
}

# create the thumbnail
if ($image_width < 4000)    //no point in resampling images larger than 4000 pixels wide - too much server processing overhead - a resize is more economical
{
    if (substr_count(strtolower($gd_version['GD Version']), "2.")>0)
    {
        //GD 2.0 
        $thumbnail = ImageCreateTrueColor($thumb_width, $thumb_height);
        imagecopyresampled($thumbnail, $image, 0, 0, 0, 0, $thumb_width, $thumb_height, $image_width, $image_height);
    } else {
        //GD 1.0 
        $thumbnail = imagecreate($thumb_width, $thumb_height);
        imagecopyresized($thumbnail, $image, 0, 0, 0, 0, $thumb_width, $thumb_height, $image_width, $image_height);            
    }    
} else {
    if (substr_count(strtolower($gd_version['GD Version']), "2.")>0)
    {
        # GD 2.0 
        $thumbnail = ImageCreateTrueColor($thumb_width, $thumb_height);
        imagecopyresized($thumbnail, $image, 0, 0, 0, 0, $thumb_width, $thumb_height, $image_width, $image_height);
    } else {
        # GD 1.0 
        $thumbnail = imagecreate($thumb_width, $thumb_height);
        imagecopyresized($thumbnail, $image, 0, 0, 0, 0, $thumb_width, $thumb_height, $image_width, $image_height);
    }
}

# insert string
if (@$_GET['tag']<>"")
{
    $font=1;
    $string= $_GET['tag'];
    $white = imagecolorallocate ($thumbnail, 255, 255, 255);
    $black = imagecolorallocate ($thumbnail, 0, 0, 0);
    imagestring ($thumbnail, $font, 3, $thumb_height-9, $string, $black);
    imagestring ($thumbnail, $font, 2, $thumb_height-10, $string, $white);
}

switch ($image_type)
{
    case 2:    # JPG
        header('Content-type: image/jpeg');
        header('Content-Disposition: inline; filename='.str_replace('/','',md5($filename.$thumb_size.$thumb_size_x.$thumb_size_y.$quality).'.jpeg'));
        @imagejpeg($thumbnail,$cache_file, $quality);
        imagejpeg($thumbnail,'',$quality);

E vi metto la prosecuzione nel prossimo post

        break;
    case 3: # PNG
        header('Content-type: image/png');
        header('Content-Disposition: inline; filename='.str_replace('/','',md5($filename.$thumb_size.$thumb_size_x.$thumb_size_y.$quality).'.png'));
        @imagepng($thumbnail,$cache_file);
        imagepng($thumbnail); 
        break;

    case 1:    # GIF 
        if (function_exists('imagegif'))
        {
            header('Content-type: image/gif');
            header('Content-Disposition: inline; filename='.str_replace('/','',md5($filename.$thumb_size.$thumb_size_x.$thumb_size_y.$quality).'.gif'));
            @imagegif($thumbnail,$cache_file);
            imagegif($thumbnail);  
        } else {
            header('Content-type: image/jpeg');
            header('Content-Disposition: inline; filename='.str_replace('/','',md5($filename.$thumb_size.$thumb_size_x.$thumb_size_y.$quality).'.jpg'));
            @imagejpeg($thumbnail,$cache_file);
            imagejpeg($thumbnail); 
        }
        break;
}

//clear memory
imagedestroy ($image);
imagedestroy ($thumbnail);

?> 

Funziona e anche bene, solo per il 95% dei casi circa. A volte infatti, delle immagini correttamente caricate sul sito e lette tramite gli appositi tag HTML non vengono trasmormate in thumbs da questo script e quindi non vengono visualizzate.

Avete idea dei motivi per cui potrebbe accadere questo? Il formato è sempre JPG e il nome del file ho provato anche a renderlo senza spazi.