use warnings;
use strict;
use Mojo::DOM;

my $data = <<'ENDDATA';
yada...yada...yada..
<img src="111">
yada...yada...yada..
<img src="222">
yada...yada...yada..
<h1>Some title</h1>
yada...yada...yada..
<a href="444444">
<img src="333">
yada...yada...yada..
<img src="444">
ENDDATA

my $dom = Mojo::DOM->new($data);
my (@imgs,$seen_h1);
for my $tag ( $dom->find('h1, img')->each ) {
	if ($seen_h1 && $tag->tag eq 'img' && length $tag->attr('src'))
		{ push @imgs, $tag }
	elsif ($tag->tag eq 'h1')
		{ $seen_h1 = 'true' }
}
print $_->attr('src'),"\n" for @imgs;

__END__

333
444