Change site logo for an specific content type
The simplest way would be to create a tpl for the content type to do that you can follow the below steps

First create a preprocess_page function as given below. This would go into the template.php file. 

function YOURTHEMENAME_preprocess_page(&amp;$vars) {
  if (isset($vars['node']-&gt;type)) {
    $vars['theme_hook_suggestions'][] = 'page__' . $vars['node']-&gt;type;
  }
}


now you can create a new page.tpl per content type something like 

page__CONTERNTTYPENAME.tpl.php


You can copy the entire content of the existing page.tpl.php into this and replace the logo with the desired logo. 

in zen theme the logo is in the page.tpl is printed as follows

&lt;?php if ($logo): ?&gt;
      &lt;a href="&lt;?php print $front_page; ?&gt;" title="&lt;?php print t('Home'); ?&gt;" rel="home" id="logo"&gt;&lt;img src="&lt;?php print $logo; ?&gt;" alt="&lt;?php print t('Home'); ?&gt;" /&gt;&lt;/a&gt;
    &lt;?php endif; ?&gt;


here you can replace the image src with the direct path to your logo.