Another approach is to shuffle a set of indices using a Schwartzian transform, and then use a subset of the randomized indices to select a subset of the images.

my @indices = map { $_->[0] }
              sort { $a->[1] <=> $b->[1] }
              map { [$_, rand()] }
              0 .. $#arr;

my @subset = @arr[@indices[0..$number_to_show - 1]];
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