Duplicate listing of post under category

I wrote a bit of code that prints all post under a category and displaying the feature image of that post.

However I’m not sure what’s wrong with my loop as it’s printing the same post X number of times. X being the number of categories I have.

Here is my code…

<?php
	$cats = get_categories();
	$thumbnails = get_posts();
	foreach ($cats as $cat) {
	    $cat_id = $cat->term_id;
	    if ( has_post_thumbnail($thumbnail->ID, $category->term_id)) {
		      echo '<li><a href="' . get_permalink( $thumbnail->ID ) . '" title="' . esc_attr( $thumbnail->post_title ) . '">';
		      echo get_the_post_thumbnail($thumbnail->ID, 'full');
		      echo '</a></li>';
	    }
	}
?>