I have writed the thumbnail function with GD.pm, if it's useful for someone..
sub make_thumbnail($$$$$;$)
{

my ($filename,$thumbnail,$width,$height,$quality,$convert)=@_;

#Try GD lib
    eval 'use GD';
    unless(@){
my $src;
my $keys;
if($filename=~/\.jpg$/) {
$src = GD::Image->newFromJpeg($filename);
}
elsif($filename=~/\.png$/) {
$src = GD::Image->newFromPng($filename);
}
else {
	system("/absolute/path/to/gif2png", "$filename"); #gif2png taken from futallaby cause i have a GDlib that doesn't support gif
	$filename =~ s/\.gif/\.png/;
	$src = GD::Image->newFromPng($filename);
   	}
my ($sW,$sH) = $src->getBounds();
my $key_w = $width / $sW;
	my $key_h = $height / $sH;
if ($key_w < $key_h) { $keys = $key_w; } 
else { $keys = $key_h; }
my $out_w = int($sW * $keys) +1;
    my $out_h = int($sH * $keys) +1;
my $thum = GD::Image->new($out_w,$out_h);
$thum->copyResized($src,0,0,0,0,$out_w,$out_h,$sW,$sH);
my $jpg_data = $thum->jpeg($quality);
open (DISPLAY,">$thumbnail");
binmode DISPLAY;
print DISPLAY $jpg_data;
    close DISPLAY;
return 1 unless($!); 

}
...