Your basic problem is that you're not updating $pics_found in your top while loop, like you are in the bottom loop. By the way, $pics_found = $#found_images + 1 is an ugly way of saying $pics_found = @found_images, since an array in scalar context returns its size. There's really no need for a separate variable, then! Also, move your $limit_img_size logic to the inside of the while loop. The two loops do the same thing, there's just a slight bit of extra logic if $limit_img_size is "yes".

while (@found < $pics_to_find * 30) {
  last unless @found_galleries;  # exit the loop if there are no more
  my $gallery_content = get(pop @found_galleries);

  while ($gallery_content =~ /.../) {
    ...

    # why use "yes" and "no"?  why not just a true value or a false va
+lue?
    next if
      $limit_img_size eq "yes"
      and !some_size_constraint();

    push @found, ...;
  }
}
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