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 = $width * .75;
    my $nheight = $height * .75;

    system "mogrify -resize ${nwidth}x$nheight $picname";
}