{
  package Backup::General;
  sub backup_file { my ($class, $file) = @_; ... }
  sub backup_dir {
    my ($class, $dir) = @_;
    opendir my $d, $dir;
    while (readdir $d) {
      next if /^\./ or -d;
      $class->backup_file($_);
    }
  }
  ...
}
{
  package Backup::ImageDir;
  use parent 'Backup::General';
  sub backup_file {
    my ($class, $file) = @_;
    $class->upload_flickr($file) if $file =~ /\.jpeg$/i;
    $class->SUPER::backup_file($file)
  }
  sub upload_flickr { ... }
  ...;
}
{
  package Backup::LogDir;
  use parent 'Backup::General';
  sub backup_dir {...}
  ...
}

##</code><code>##

use Config::Tiny;
use Module::Runtime qw(use_package);

my $config = Config::Tiny->read("$dir/backup.ini");
my $class  = $config->{_}{backup_class} || 'Backup::General';
use_package($class)->backup_dir($dir);