image.php Bilddarstellung mit Navigation

<?php if (wp_attachment_is_image($post->id)) {
                                    $att_image = wp_get_attachment_image_src( $post->id, "medium");
                                    ?>
                                    <p class="attachment">
                                        <a href="<?php echo wp_get_attachment_url($post->id); ?>" title="<?php the_title(); ?>">
                                        <img src="<?php echo $att_image[0];?>" width="<?php echo $att_image[1];?>" height="<?php echo $att_image[2];?>"  class="attachment-medium" alt="<?php $post->post_excerpt; ?>" />
                                        </a>
                                    </p>
                                <?php } ?>