Moving onto my next problem.

As this question is unrelated to the rest of the thread, it'd have been better to post it in a new thread.

You don't need to construct a new Image::Magick over the argument passed to the subroutine. The normal way to handle arguments is (see perlsub):

sub ImageNotDark {
  my ($iutImage,$arg2,$arg3,...) = @_;
  # --OR--
  my $iutImage = shift;
  my $arg2 = shift;
  ...
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Or, if your intention were to work with a copy of the image in the subroutine, you could simply do my $imgCopy = $_[0]->Clone(); inside the subroutine.