Allow ‘Set featured images’ to select multiple images

Question

Its certainly not a few liner code. So its better to use a Feature Gallery plugin. I just tried that which works perfectly fine and you can use below code to get the images in Featured Gallery.

<?php $galleryArray = get_post_gallery_ids($post->ID);  
      foreach ($galleryArray as $id) { ?>   
         <img src="https://wordpress.stackexchange.com/questions/205062/<?php echo wp_get_attachment_url( $id ); ?>"> 
<?php }?>

Please refer plugin description to get more details about the code.