use Regexp::List;
print Regexp::List->new->list2re(qw(

image_sequenceA.1.tif
image_sequenceA.2.tif
image_sequenceA.3.tif
image_sequenceB.40.tif
image_sequenceB.41.tif
image_sequenceB.42.tif

));
__END__
(?^:image_sequence(?:A\.[123]\.tif|B\.4[012]\.tif))