Replace Missing Thumbnail

// Replace Missing Thumbnail / Kiri Vadivelu / 2026

function replace_missing_thumbnail( $html, $post_id, $post_thumbnail_id, $size, $attr ) {

    if ( empty( $html ) ) {

        // Replace with your site logo URL

        $logo_url = 'https://example.com/path/to/logo.png';

        $html = '<img src="' . esc_url( $logo_url ) . '" alt="Site Logo" />';

    }

    return $html;

}

add_filter( 'post_thumbnail_html', 'replace_missing_thumbnail', 10, 5 );