Reader Feed with image

i have 2 website and i add in that 2 site FEED READER RSS

in SITE 1 i add FEED READER from SITE 2
and
in SITE 2 i add FEED READER from SITE 1

with same CODE:

<?php
$rss = fetch_feed('feeeeeeed URL');

if (!is_wp_error( $rss ) ) : 

    $maxitems = $rss->get_item_quantity(6);
    $rss_items = $rss->get_items(0, $maxitems);
endif;
?>
<?php function get_first_image_url($html)
 {
 if (preg_match('/<img.+?src="(.+?)"/', $html, $matches)) {
 return $matches[1];
 }
 }
?> 

    <?php
     if ($maxitems == 0) echo '';
     else
     foreach ( $rss_items as $item ) : ?>
 <article>
<div class="articol" >
<h2><a target="_blank" href='<?php echo esc_url( $item->get_permalink() ); ?>' title='<?php echo esc_html( $item->get_title() ); ?>'> <?php echo esc_html( $item->get_title() ); ?></a></h2>
<div class="art-img relative">
<a target="_blank" href='<?php echo esc_url( $item->get_permalink() ); ?>' title='<?php echo esc_html( $item->get_title() ); ?>'>
<?php echo '<img src="' .get_first_image_url($item->get_content()). '"/>'; ?>
</a>
</div>
</div>
    <?php endforeach; ?>

in site 1 appear IMAGE , in site 2 no appear image, why? can explain? or help me ?