FacetWP – checkbox facet to show posts with images

<?php

add_filter( 'facetwp_index_row', function( $params, $class ) {
    if ( 'has_image' == $params['facet_name'] ) {
        $post_id = (int) $params['post_id'];

        if ( has_post_thumbnail( $post_id ) ) {
            $params['facet_value'] = 1;
            $params['facet_display_value'] = 'Has photos';
        }
        else {
            $params['facet_value'] = ''; // skip indexing this row
        }
    }
    return $params;
}, 10, 2 );