{
		open (DATA, ">>$file") or die "Can't create File: $file\n";
		close(DATA);
	}
}

sub generate_random_string
{
	ref(my $self = shift) or croak "instance variable needed";
	my $length = shift;

	# generate a new code
	my $code = "";
	for(my $i=0; $i < $length; $i++)
	{ 
		my $char;
		my $list = int(rand 4) +1;
		if ($list == 1)
		{ # choose a number 1/4 of the time
			$char = int(rand 7)+50;
		} else { # choose a letter 3/4 of the time
			$char = int(rand 25)+97;
		}
		$char = chr($char);
		$code .= $char;
	}
	return $code;
}

sub _save_code
{
	ref(my $self = shift) or croak "instance variable needed";
	my $code = shift;
	my $md5 = shift;

	my $database_file = File::Spec->catfile($self->data_folder(),'codes.txt');

	# set a variable with the current time
	my $current_time = time;

	# create database file if it doesn't already exist
	$self->_touch_file($database_file);

	# clean expired codes and images
	open (DATA, "<$database_file")  or die "Can't open File: $database_file\n";
		flock DATA, 1;  # read lock
		my @data=<DATA>;
	close(DATA);
	
	my $new_data = "";
	foreach my $line (@data) 
	{
		$line =~ s/\n//;
		my ($data_time,$data_code) = split(/::/,$line);
		if ( (($current_time - $data_time) > ($self->expire())) ||
		     ($data_code  eq $md5) )
		{	# remove expired captcha, or a dup
			my $png_file = File::Spec->catfile($self->output_folder(),$data_code . ".png");
			unlink($png_file) or carp("Can't remove png file [$png_file]\n");
		} else {
			$new_data .= $line."\n";
		}
	}
	
	# save the code to database
	warn "open File: $database_file\n" if($self->debug() >= 2);
	open(DATA,">$database_file")  or die "Can't open File: $database_file\n";
		flock DATA, 2; # write lock
		warn "-->>" . $new_data . "\n" if($self->debug() >= 2);
		warn "-->>" . $current_time . "::" . $md5."\n" if($self->debug() >= 2);
		print DATA $new_data;
		print DATA $current_time."::".$md5."\n";
	close(DATA);
	warn "Close File: $database_file\n" if($self->debug() >= 2);

}

sub create_image_file
{
	ref(my $self = shift) or croak "instance variable needed";
	my $code = shift;
	my $md5 = shift;

	my $length = length($code);
	my $im_width = $self->width();
	# create a new image and color
	my $im = new GD::Image(($im_width * $length),$self->height());
	my $black = $im->colorAllocate(0,0,0);

	# copy the character images into the code graphic
	for(my $i=0; $i < $length; $i++)
	{
		my $letter = substr($code,$i,1);
		my $letter_png = File::Spec->catfile($self->images_folder(),$letter . ".png");
		my $source = new GD::Image($letter_png);
		$im->copy($source,($i*($self->width()),0,0,0,$self->width(),$self->height()));
		my $a = int(rand (int(($self->width())/14)))+0;
		my $b = int(rand (int(($self->height())/12)))+0;
		my $c = int(rand (int(($self->width())/3)))-(int(($self->width())/5));
		my $d = int(rand (int(($self->height())/3)))-(int(($self->height())/5));