How to tell if Jetpack's Photon is active?

Question

There are multiple ways to identify if a plugin is active (here's one) but how can we identify if a specific JetPack component is active, for example Photon?

Answer 1

Checking for the option value jetpack_active_modules.

^{Searching for photon in wp_options is how I found the option_name.}

---

The following prints the option as an admin notice:

add_action( 'admin_notices', 'wpse_75103_active_jetpack_modules' );

function wpse_75103_active_jetpack_modules() 
{
    if( !current_user_can( 'delete_users' ) )
        return;

    $jetp = get_option( 'jetpack_active_modules' );

    $photon_active = ( in_array( 'photon', $jetp ) ) ? 'is' : 'is not';
    echo '<h1>Photon ' . $photon_active . ' active</h1>';

    echo '<h2>All JetPack Options</h2>';
    echo '<pre>' . print_r( $jetp, true ) . '</pre>';
}

---

The following is the result with all modules activate.
The key numbers are in the order by which the modules were activated and should not be used as reference. And I don't know what logic is behind them.
^{( in a local host installation )}

Array
(
    [0] => vaultpress
    [1] => photon
    [3] => notes
    [5] => publicize
    [7] => stats
    [9] => comments
    [11] => subscriptions
    [13] => post-by-email
    [15] => carousel
    [17] => sharedaddy
    [19] => after-the-deadline
    [21] => infinite-scroll
    [23] => enhanced-distribution
    [25] => json-api
    [27] => mobile-push
    [29] => widgets
    [31] => latex
    [33] => gravatar-hovercards
    [35] => contact-form
    [37] => minileven
    [39] => custom-css
    [41] => shortcodes
    [43] => shortlinks
)