I found that $text needs to be an exact match. I would prefer not having to use exact matches. I added case insensitivity to it also.

This suggests to me that you might be performing the match the wrong way round, i.e. you want to look case-insensitively within $text for things which match the patterns held in @big_images. If that's the case then you need to switch the grep so that $_ becomes the pattern. e.g.:

$class .= ' right' unless grep($text =~ /$_/i, @big_images);
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Here's the SSCCE:

use strict;
use warnings;

use Test::More tests => 4;

my $text = 'Only smartees have the answer!';
ok grep ($text =~ /$_/i, 'Smart'), 'Case-insensitive match';
ok grep ($text =~ /$_/i, 'foo', 'Smart', 'bar'), 'Match one of three';
ok grep ($text =~ /$_/i, 'foo', 'Smart', 'art'), 'Match two of three';
ok !grep ($text =~ /$_/i, 'foo', 'baz'), 'Match none';
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HTH.