as it looks like you are populating a hash, this should work

your code

$image->Draw( fill=>'rgba(100,0,0,0.55)', primitive=>'rectangle', points=>'$box_left_x,$box_left_y $box_x,$box_y' );

New code

$image->Draw( fill     =>'rgba(100,0,0,0.55)',
              primitive=>'rectangle',
              points   =>$box_left_x,$box_left_y,
                         $box_x,$box_y 
);
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