Laravel validation rules if field empty another field required

I have a Laravel 5.3 app, and an update form where I send user profile values. One of them is user image as well, I am creating a hidden input field for it, so if the user is not uploading any new image, I can still see that he has the hidden field with the old image value.

<input type="hidden" class="form-control" name="old_image" value="{{ $player->image_filename }}" id="oldImage">

If he removes the image, the hidden input value becomes empty.

document.getElementById('oldImage').value = '';

That is how I thought of updating a user image. But I don't know how to set up validation rules for that form. Something that would be similar to this:

    public function rules()
    {
        return [
          'first_name' => 'required|max:50',
          'last_name' => 'required|max:50',
          'birthday' => 'required',
          'image' => required if old_image empty
        ];
    }