use Image::Size;

my $fname = "filelist.txt";

open (IN, $fname) || die "can't open $fname\n";

while (<IN>) {
    chomp;
    push @files, $_;
}

foreach $picname (@files) {

    my ($width, $height) = imgsize($picname);
    return unless $width;
    print "making thumbnail for $width x $height $picname\n";
    my $nwidth = 600;
    my $nheight = 450;
    if ($height > $width) {
	$nwidth = 450;
	$nheight = 600;
    }
    system "mogrify -resize ${nwidth}x$nheight $picname";
}