add_action('woocommerce_before_checkout_form', 'displays_cart_products_feature_image');
function displays_cart_products_feature_image() {
    foreach ( WC()->cart->get_cart() as $cart_item ) {
        $product = $cart_item['data'];
        if(!empty($product)){
            // $image = wp_get_attachment_image_src( get_post_thumbnail_id( $product->ID ), 'single-post-thumbnail' );
            echo $product->get_image();

            // to display only the first product image uncomment the line below
            // break;
        }
    }
}