Changing "Submit" form button to an image

[zetetic]

I have a couple form submit buttons that came along with a mod I just installed that I want to replace with graphic images. I'm pretty sure there's a little Javascript workaround to make that happen I just don't quite get how to make it work. Any ideas?

Here's the code currently:

<form method="post" action="journal.php?$session[sessionurl]do=comments&journalid=$journalid">

<input class="button" type="submit" value="Show comments" /></form>