base href = subfolder

For web development testing purposes (of a blog that resides in the root of the main domain), I have a testing blog at http://subdomain.domain.com/subfolder.

In header.php, I have set a base href:

<base href="<?php echo get_settings('siteurl'); ?>" />

Everything works well except images are missing. The code I have tried is:

<img src="wp-content/themes/default/images/image.gif" />

and

<img src="/wp-content/themes/default/images/image.gif" />

The base href is getting ignored and image.gif wants to be found at:

http://subdomain.domain.com/wp-content/themes/default/images/banner.gif

The difference is that /subfolder is missing. Any ideas how to get this fixed without adding /subfolder to the img src code?

i.e. <img src="/subfolder/wp-content/themes/default/images/banner.gif" />

I don’t want to do that because when I copy files over to the live blog, then I’d have to remove /subfolder from everything.