#!/usr/bin/perl
use v5.14;

use HTML::Template;
my $template = HTML::Template->new(filename => 'gallery.tmpl');

my @gallery;
for my $count (1..3) {
    my %data = (
        img_small => "img$count-small.jpg",
        img_big   => "img$count-big.jpg",
    );
    push @gallery, \%data;
}

$template->param(DESCR   => "Some general description");
$template->param(GALLERY => \@gallery);

print $template->output;