Highlight parent menu item when child post

to highlight the menu element, you should add the class active. This will work for your photo custom post type.

Concerning your blog posts:
As you can see, in the URL of a blog post there is no post/ which would be necessary for your code to act on. Furthermore, the blog overview page does not equal the custom post rewrite slug.

You could use something like this statement to add the active class for blog posts:

if ( 
     'post' === get_post_type($post->ID) 
     && false !== strpos( $menu_slug, 'blog' )
) {
    $classes[] = 'current-menu-item';
    $classes[] = 'active';
}