5.x

This is a pretty simple task but one I seem to end up doing over and over again for whatever project I'm working on at the time. I've done it a number of ways, from simply using CSS and dealing with multiple cross-browser issues, and probably quite a few alterations of this technique.

In our custom module we're going to need a couple functions. First, we need to use hook_elements to define our new image element.


function siteconfig_elements() {
$type['image_button'] = array(
'#input' => TRUE,
'#button_type' => 'submit',
);
return $type;
}
?>


Next, we need to theme our new type of element, which is called image_button above.


function theme_image_button($element) {
return '\n";
}
?>

This is a very similar to Drupal's core theme_button function.

This function is needed to ensure the default_value doesn't get moved to #value. This should solve the issue with multiple submit buttons some browsers have.


function image_button_value() {
// null value to guarantee default_value doesn't get moved to #value }
?>

Next, we need to use our trusty old hook_form_alter for the submit button of our choice.


function siteconfig_form_alter($form_id, &$form) {
if ($form_id == 'myformid') {
$form['submit'] = array(
'#type' => 'image_button',
'#image' => base_path() . path_to_theme() .'/images/search-btn.gif',
'#title' => t('Search'),
'#default_value' => t('Search'),
);
}
}
?>

Voila! Thanks chx and merlinofchaos. ;)