laravel 5.4 embed image in mail

I have just upgraded my 5.2 install of laravel to 5.3 and then to 5.4 following the official upgrading methods.

I am now trying to use one of the new features, to create a markdown formated email.

According to the documentation found at: https://laravel.com/docs/5.4/mail#view-data

To embed an inline image, use the embed method on the $message variable within your email template. Laravel automatically makes the$message variable available to all of your email templates, so you don't need to worry about passing it in manually:

However, this:

<img src="{{ $message->embed(public_path().'/img/official_logo.png') }}">

will produce the following error:

Undefined variable: message

Am I missing something? Or is there something undocumented in the upgrading guides?

Later edit:

I am calling the email function with:

\Mail::to($user)->send(new WelcomeCandidate($user, $request->input('password')));

And WelcomeCandidate looks like:

<?phpnamespace App\Mail;use Illuminate\Bus\Queueable;use Illuminate\Mail\Mailable;use Illuminate\Queue\SerializesModels;use Illuminate\Contracts\Queue\ShouldQueue;use App\Models\User;class WelcomeCandidate extends Mailable{    use Queueable, SerializesModels;    public $user;    public $password;    /**     * Create a new message instance.     *     * @return void     */    public function __construct(User $user, $password)    {        //        $this->user = $user;        $this->password = $password;    }    /**     * Build the message.     *     * @return $this     */    public function build()    {        $this->subject('Welcome!');        return $this->markdown('emails.welcome-candidate');    }}