First, you're using perl, not php. ['asdf'] will evaluate as 0, {'asdf'} is how perl accesses hashes.
I would suspect you want something like:
Code:
#!/usr/bin/perl
my $range = 13;
my $random_number = int(rand($range));
$image[1]='example.banner.jpg';
$link[1]='http://some.domain';
$image[n]='example.banner.jpg';
$link[n]='http://some.domain';
$data .= '<a href="'. $link[$random_number] . '">';
$data .= '<img src="'. $image[$random_number] . '" border=0>';