I have figured out, with a lot of searching and reading, how to change the next/previous links into images with regards to the blog archives...
<div class="navigation"> <?php previous_posts_link('<img src="/images/previous.png"/>') ?> <?php next_posts_link('<img src="/images/next.png"/>') ?> </div>
...but I can't for the life of me figure out how to do the same on individual pages. I see that this...
<?php wp_link_pages(array('before' => 'Pages: ', 'next_or_number' => 'next')); ?>
...is the original code, but I have absolutely no idea how to replace the output with the same previous and next images that I'm using on the blog archives.
Can someone point me in the right direction, (or post the code I need if you're feeling especially generous), please?