This is quite a cool article I saw a while back on the forgotten <button> element, which is something that I didn't know about.

Most html writers will be familiar with:

<input type="submit" name="test" value="Click Me" />

Suppose though, that you want to make a clickable image. You can use some CSS markup, but instead with the button element, you can also do something like...

<button type="submit" name="test" value="Click Me">
  <img src="images/click_me.jpg" alt="Click Me" />
</button>

I'm not quite sure on how the best way to deal with screen readers or text-based browsers is, but the alt tag should work fine for that. If not, perhaps a hidden span inside the button element would work better.