mogrify  crop 200x200+0+0 -gravity center file.jpg

##</code><code>##

my $image = Image::Magick->new;
$image->Read($file);

my ($width, $height) = $image->Get('width', 'height');

if($width < $height) {
  my $nh = $size*$height/$width;
  $image->Resize(width => $size, height => $nh);
} else {
  my $nw = $size*$width/$height;
  $image->Resize(width => $nw, height => $size);
}

$image->Crop(width => $size, height => $size);

##</code><code>##

$image->Set(Gravity => 'Center');