How to get the URL of a file located in the theme folder?
You can use drupal_get_path() to get the path to your theme folder:

$path = drupal_get_path('theme', 'name_of_theme');


From there you can specify a particular file like this:

$image_path = $path . '/images/image.jpg';


You could also use path_to_theme(), but be wary as the return from this can change depending on the context it's called in:


  It can point to the active theme or the module handling a themed implementation. For example, when invoked within the scope of a theming call it will depend on where the theming function is handled. If implemented from a module, it will point to the module. If implemented from the active theme, it will point to the active theme. When called outside the scope of a theming call, it will always point to the active theme.