You can do it like so, I guess:

    <div class="alignleftfp">
        <?php next_post_link('%link', '<img class="imgalign" src="' . WP_CONTENT_URL . '/uploads/1.png" alt="Next" /> %title'); ?>
    </div>
    <div class="alignrightfp">
        <?php previous_post_link('%link', '%title <img class="imgalign" src="' . WP_CONTENT_URL . '/uploads/1.png" alt="Next" />'); ?>
    </div>

PS. You shouldn't use `next_post`/`previous_post` functions - they're deprecated.