using
$img = new Imagick();
$img->readImage( $local_da_imagem );
print_r( $img->getImageCompressionQuality() );
(PECL imagick 2 >= 2.2.2, PECL imagick 3)
Imagick::getImageCompressionQuality — Gets the current image's compression quality
Gets the current image's compression quality
Returns integer describing the images compression quality