How to fetch all WordPress posts with featured image?
This should work:
$loop = new WP_Query( array( 'posts_per_page' => -1, 'meta_key' => '_thumbnail_id' ) );I haven't tested this, though. Also, this will probably fetch all posts and pages. Use 'post_type' => 'post' to limit it to blog posts.
I don't believe you need any special loops defined for that to work.
Though you do need to add some small snippets into your functions.php
like this one:
<?php add_theme_support ( 'post-thumbnails' ); ?>after apply the above code to functions.php file, your theme will support Featured Images and you will see a new link @ the bottom right of your Post Add / Edit interface.
This guide will help you, if you are looking for more info regarding this : How to Use Wordpress Featured Image Feature