TIMTOWTDI. Here's an approach using a for loop.

use strict;
use warnings;

use Test::More tests => 1;

my @have = qw/00204597_957.tif 00271558_148.tif 00271558_585.tif/;
my @want = qw/00204597_957 00271558_148 00271558_585/;

s/\..*// for @have;
is_deeply \@have, \@want;
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