there may be several duplications...

Not enough information. Do you mean:

1 Duplicated names in the array? (eg dad_and_brittney.jpg occurs more than once?). In that case, pre-process your array to exclude such duplicates:

# Assume @all_pics to be your array
my %seen;
@all_pics = grep !$seen{$_}++, @all_pics;
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2 You don't want to display a picture that has already been shown?

3 You have duplicate pictures with different names? That's a whole 'nother problem...