[support] HTML displayed as text

I'm trying to edit my primary links menu to replace the text with a button image, and I'm having a problem with getting my <img> tag to display. I've overridden the theme_menu_links() function in template.php, and it looks like what I need to do is replace $link['title'] with the <img> tag. To do this, I added this line to the function:

$link['title'] = "<img src="images/btn_home.jpg">";

However, the whole tag is displayed as text on the page, and when I view source, this is what I see for the link:

<li><a href="/drupal57/" title="Home page" class="active">&lt;img src=&#039;images/btn_home.jpg&#039;&gt;</a></li>

I don't understand this, because in other places in the function, that is how tags are written out in the code. What do I need to change to get the actual quotes and < > symbols written out correctly?

Thanks.

Steve