extra_attr support

I can’t get extra_attr work. Any suggestion?

<?php
$args = array(
	'class'					=> 'alignleft',
	'extra_attr'		=> 'itemprop="image"',
);
echo get_avatar( get_the_author_meta( 'ID' ), 96, null, null, $args );
?>

https://www.ads-software.com/plugins/metronet-profile-picture/