Automatic Alt Text With Spatie Media Package and AWS Rekognition

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I recently implemented a feature in our API that automatically creates alt tags for all images uploaded with Spatie Laravel-medialibrary. This allows all images added to automatically be tagged with AWS's Rekgonition API, saving our marketing team hundreds of hours per year.

Getting Started

This is how the feature works:

  1. We start with Spatie\MediaLibrary\MediaCollections\Events\MediaHasBeenAdded event that fires when a new media item is added.
  2. Next, we listen for that event in our AutoAltTagListener listener class.
  3. Using Laravel's DI container, we will inject our AltTagService into the handler.
  4. That service will call AWS Rekognition API to provide the image tags for the image.

Screen Shot 2021-01-01 at 1.43.10 PM.png

Could you handle everything in the listener?

Of course. But, we want to decouple the auto alt tagging logic into a service, so that we could use it in other areas of the application by registering a service provider.

Step 0 - Setup AWS IAM permissions for AWS Rekgonition

For this service to work, the AWS credentials you've provided in your application need to have permissions to use the AWS Rekognition API.

Step 1 - Add Rekognition Client Configs

So that you can follow along, I've organized this project to have the credentials for AWS Rekognition in our config/services.php file, under the index of rekognition:

// config/services.php
// ...
    'rekognition'   => [
        'key'    => env('AWS_ACCESS_KEY_ID'),
        'secret' => env('AWS_SECRET_ACCESS_KEY'),
        'region' => env('AWS_DEFAULT_REGION', 'us-east-1'),
    ],

Step 2 - Create the service

This portion is a bit up to you, but I like to create a app/Services folder. Assuming that structure, let's create a file app/Services/AltTagService.php

Within that file, this is what we want our service to look like:

<?php

namespace App\Services;

use Aws\Credentials\Credentials;
use Aws\Rekognition\RekognitionClient;
use Illuminate\Support\Facades\Http;

class AltTagService
{
    protected $rekognition;

    public function __construct()
    {
        $rekognitionCreds  = config('services.rekognition');
        $credentials       = new Credentials($rekognitionCreds['key'], $rekognitionCreds['secret']);
        $this->rekognition = new RekognitionClient([
            'credentials'   => $credentials,
            'region'        => $rekognitionCreds['region'],
            'version'       => 'latest'
        ]);
    }

    public function getAltTags(string $url)
    {
        $response = Http::get($url);
        if($response->successful())
        {
            $result   = $this->rekognition->detectLabels([
                'Image' => [
                    'Bytes' => $response->body()
                ],
                'MaxLabels'     => 12,
                'MinConfidence' => 65.00,
            ]);
            $prefix = 'Image of ';
            return $prefix . collect($result->toArray()['Labels'])->implode('Name', ', ') . '.';
        }
    }
}

Step 3 - Register Service Provider

We'll run

php artisan make:provider AltTagServiceProvider

This will create a file at app/Providers/AltTagServiceProvider.php

Then, we'll want this file to look like this:

<?php

namespace App\Providers;

use App\Services\AltTagService;
use Illuminate\Support\ServiceProvider;

class AltTagServiceProvider extends ServiceProvider
{
    /**
     * Register services.
     *
     * @return void
     */
    public function register()
    {
        $this->app->singleton(AltTagService::class, function ($app) {
            return new AltTagService();
        });
    }

    /**
     * Bootstrap services.
     *
     * @return void
     */
    public function boot()
    {
        //
    }
}

If you'd like to learn more about binding to the service container, check out Binding Basics

Great! Now, we can access this service anywhere in the app through the container.

Step 4 - Create the listener

Next, let's run:

php artisan make:listener Media/AutoAltTagListener

This will create a file in app/Listeners/Media/AutoAltTagListener.php.

Here's where we will call the service we registered above in the constructor of our listener in the following code:

<?php

namespace App\Listeners\Media;

use App\Services\AltTagService;
use Illuminate\Contracts\Queue\ShouldQueue;
use Illuminate\Queue\InteractsWithQueue;
use Spatie\MediaLibrary\MediaCollections\Events\MediaHasBeenAdded;

class AutoAltTagListener
{
    protected $altTagService;

    /**
     * Create the event listener.
     *
     * @return void
     */
    public function __construct(AltTagService $altTagService)
    {
        $this->altTagService = $altTagService;
    }

    /**
     * Handle the event.
     *
     * @param  object  $event
     * @return void
     */
    public function handle(MediaHasBeenAdded $event)
    {
        if (! $event->media->hasCustomProperty('alt')) {
            $event->media
            ->setCustomProperty('alt', $this->altTagService->getAltTags( $event->media->getUrl() ))
            ->save();
        }
    }
}

Step 5 - Register the event listener

Nothing special here, we're just going to register the listener as we would any other in our EventServiceProvider.php:

        Spatie\MediaLibrary\MediaCollections\Events\MediaHasBeenAdded::class => [
            \App\Listeners\Media\AutoAltTagListener::class
        ]

Conclusion

You can now upload files with the Spatie media library. The alt tag should be available on any media model via the getCustomProperty method.

An example:

$altTag = $myMediaModel->getCustomProperty('alt');

Enjoy!

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