Validate a base64 decoded image in laravel

Im trying to get a image from a PUT request for update a user picture(using postman), and make it pass through a validation in Laravel 5.2, for making the call in postman use the following url:

http://localhost:8000/api/v1/users?_method=PUT

and send the image string in the body, using a json like this:

{
    "picture" : "data:image/png;base64,this-is-the-base64-encode-string"
}

In the controller try a lot of differents ways for decode the image and try to pass the validation:

1. First I tried this:

   $data = request->input('picture');
   $data = str_replace('data:image/png;base64,', '', $data);
   $data = str_replace(' ', '+', $data);
   $image = base64_decode($data);
   $file = app_path() . uniqid() . '.png';
   $success = file_put_contents($file, $image);
   

2. Then I tried this:

   list($type, $data) = explode(';', $data);
   list(, $data) = explode(',', $data);
   $data = base64_decode($data);
   $typeFile = explode(':', $type);
   $extension = explode('/', $typeFile[1]);
   $ext = $extension[1];
   Storage::put(public_path() . '/prueba.' . $ext, $data);
   $contents = Storage::get(base_path() . '/public/prueba.png');
   

3. Try to use the intervention image library (http://image.intervention.io/) and don't pass:

   $image = Image::make($data);
   $image->save(app_path() . 'test2.png');
   $image = Image::make(app_path() . 'test1.png');
   

This is the validation in the controller:

    $data = [
        'picture' => $image,
        'first_name' => $request->input('first_name'),
        'last_name' => $request->input('last_name')
    ];

    $validator = Validator::make($data, User::rulesForUpdate());
    if ($validator->fails()) {
        return $this->respondFailedParametersValidation('Parameters failed validation for a user picture');
    } 

this is the validation in the User-model:

public static function rulesForUpdate() {
    return [
        'first_name' => 'max:255',
        'last_name' => 'max:255',
        'picture' => 'image|max:5000|mimes:jpeg,png'
    ];
}