Yes, Image::Magick will easily scale images and maintain the size proportions if you use the Scale method. Here's how you would accomplish that:

# Thumbnail Dimensions
my ($thumb_max_height, $thumb_max_width) = (100,100);

my $p = new Image::Magick;
$p->Read($image_file);
$p->Scale(geometry => "${thumb_max_height}x${thumb_max_width}");
$p->Write($thumb_file);
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- Miller