Template suggestion via preprocess_page and the Image Gallery module

I'm currently using a custom template page for image pages, namely page-image.tpl.php. It works fine.

But the page-image.tpl.php file is an exact copy of another template file and I don't want to have multiple copies of the same page template.

So I tried in template.php, the preprocess_page function, to make a suggestion.

I can get it to work using if $variables['title'] == 'Image galleries' then use this template, but I don't like using the title since that is so arbitrary.

I'm looking for a variable that definitively identifies the image page and image galleries.

I tried $node, $page, $term, $form... No good.

Same goes for the contact module page. Any suggestions?

Thanks in advance.