WP dynamic featured image - Can't get second featured image url

I'm actually working on a wordpress website with a Dessign.net theme (the pixel one) which got a beautiful full-page slider on the front page. The slider shows the featured image of selected posts (post for which i've checked "show in slideshow" in the meta box field on edit page).

Those featured image are used in the same way for different view on the site (eg. thumbnails). I need them for the thumbnails, but i'ld like another image (still relative to selected posts) for the home-page slider.

I've found that "Dynamic Featured Image" plugins for wordpress but now i can't achieve to get the second featured image url in the slider's loop.

Here's the part of code for the slider, as it was with the theme:

<ul>
        <?php
        $slider_arr = array();
        $x = 0;
        $args = array(
             //'category_name' => 'blog',
             'post_type' => 'post',
             'meta_key' => 'ex_show_in_slideshow',
             'meta_value' => 'Yes',
             'posts_per_page' => 99
             );
        query_posts($args);
        while (have_posts()) : the_post();



             $thumb = wp_get_attachment_image_src( get_post_thumbnail_id(get_the_ID()), 'full' );
            //$thumb = wp_get_attachment_image_src( get_post_thumbnail_id(get_the_ID()), 'large' );
            $img_url = $thumb['0'];
        ?>
            <li data-background="<?php echo $img_url; ?>" onclick="location.href='<?php the_permalink(); ?>';" style="cursor:pointer;">

            </li>
        <?php array_push($slider_arr,get_the_ID()); ?>
        <?php $x++; ?>
        <?php endwhile; ?>
        <?php wp_reset_query(); ?>

    </ul>

Now i've tried to put the code found on the plugin github page:

if( class_exists('Dynamic_Featured_Image') ) {
               global $dynamic_featured_image;
              $thumb = $dynamic_featured_image->get_featured_images( );

                        //You can now loop through the image to display them as required

              }

in place of $thumb = wp_get_attachment_image_src( get_post_thumbnail_id(get_the_ID()), 'full' );

But $thumb return array as a string

I tried a few different things but i'm not fluent in php.

Hope this is understandable.

I had to recently look for answers on something like this myself. The plugin author is great at explaining how to actually set up the plugin, but doesn't really say how to get the images, leaving it up to the developer. So, I feel you.

If I understand you correctly, you need to get the featured image from the plugin, not the featured image included in WordPress.

<?php global $dynamic_featured_image;
$featured_images = $dynamic_featured_image->get_featured_images( get_the_ID() );

//You can now loop through the image to display them as required
foreach($featured_images as $featured_image) {

echo "<a href='".get_the_permalink()."' class='slide'>";
echo "<span> <img src='".$featured_image['full']."' /> </span>";
echo "</a>";

} ?>

In this plugin, you can create infinite amounts of featured images per post/page. This code above is only for grabbing the first image created by the plugin. It's $featured_image['full'] that calls the image itself.

You can change the type of image shown to other sizes as well, including any custom sizes you create. The code to use those sizes can be found on this post.