function category_recent(){
    $cate = get_the_category();
    $current_cat_id = $cate[0]->cat_ID;
    $category = new WP_Query('cat='.$current_cat_id);

    $list = "<ul class='recent-posts'>";
    while($category->have_posts()){
       $category->the_post();
       $upload_dir = wp_upload_dir();

       $post_data = get_post($post->ID, ARRAY_A);
       $slug = $post_data['post_name'];
    ?>
<li>
    <div class='recentthumb'>
        <a href='<?php the_permalink() ?>' rel='bookmark' title='<?php the_title_attribute(); ?>'>
            <img src='<?php echo esc_url($upload_dir[baseurl])?>/2015/08/<?php echo $slug;?>.jpg' width='196' height='110' alt='<?php the_title_attribute(); ?>' />
        </a>
        <a href='<?php the_permalink() ?>' rel='bookmark' title='<?php the_title_attribute(); ?>'><?php the_title_attribute(); ?></a>
    </div>
</li>
<?php
}
wp_reset_query();
return $list . '</ul>';
}
add_shortcode('recent-post', 'category_recent');

<a href="'.$path.'/category_popularity" class="cat_popular">Popular</a>