http://ask.metafilter.com/200208/Want-to-create-a-cover-gallery

cbrcover.pl

#!/usr/bin/env perl
use strict;
use warnings;

use File::Basename;

my $cbrfile = $ARGV[0] or die "Usage: $0 <cbrfile>\n";

# get a verbose basic list of archive contents. (path/to/file.ext)
my $pid = open my $fh, '-|', rar => vb => $cbrfile
    or die "rar list failed: $!\n";
my @output = <$fh>;
waitpid $pid, 0;
chomp @output;

# extract first file in list.
my $first = shift @output;
system rar => e => $cbrfile, $first
    and die "rar extract failed.\n";

# extract basefilename (without path) and type extension.
my $firstbase = basename $first;
my ($ext) = $firstbase =~ m/\.(\w+)$/;

# foobar.cbr yields foobar_cover.ext
my $cover = $cbrfile;
$cover =~ s/\.cbr$/_cover.$ext/;

rename $firstbase, $cover or die "can't rename: $!";