Example:
<?php
$base_image = new Imagick('example.png');
$rect = new ImagickDraw();
$rect->setFillColor(new ImagickPixel("#EEEEEE"));
$rect->setFillOpacity(0);
$rect->setStrokeColor(new ImagickPixel("#FF0000"));
$rect->setStrokeDashArray(array(5,5,5));
$rect->rectangle(10, 10, 100, 100);
$base_image->drawImage($rect);
header('Content-type: image/png');
echo $base_image->getImage();
exit();
?>