Let's say we have this form:
<form>
<input type="text" name="some_name" value="val" id="some_name">
<input type="image" value="action" alt="Add To Cart" name="add" src="/images/submit.gif">
<input type="image" value="action" alt="Shop some more" name="return" src="/continue_shopping.gif">
</form>
How do I find the input that submitted the form?