Check Image Size

<?php
    $featuredPosts = new WP_Query( array(
        'post_type' => array( 'post','collective_slideshow' ),
        'posts_per_page' => 10,
        'orderby' => 'rand'
    ));
?>
<?php while($featuredPosts->have_posts()) : $featuredPosts->the_post();  ?>

    <?php $args = array(
            'post_type' => 'attachment',
            'numberposts' => 1,
            'post_status' => null,
            'post_parent' => $post->ID,

            );
            $attachments = get_posts($args);
            foreach ($attachments AS $attachment) {
            $imgid = $attachment->ID;
            $meta = wp_get_attachment_metadata($imgid);
            $imgw = $meta['sizes']['collective-slide']['width'];
            if ($imgw == "870") {?>
            <div class="slide">
                <div class="slideshow title">
                    <h2><?php echo get_the_title($post->post_parent); ?></h2>
                </div><!-- .title -->
                <div class="image">
                    <?php echo the_post_thumbnail('collective-slide'); ?>
                </div><!-- .image -->
            </div><!-- .slide -->
            <?php
            }
            }
    ?>

<?php endwhile; ?>