Validate a base64 decoded image in laravel

If you are using Intervention anyways, then you can leverage it for a custom validation rule. I have one called "imageable". It basically makes sure that the input given will be able to be converted to an Intervention image. Base64 data image strings will pass. A string of "foo" will not.

Validator::extend('imageable', function ($attribute, $value, $params, $validator) {
    try {
        ImageManagerStatic::make($value);
        return true;
    } catch (\Exception $e) {
        return false;
    }
});

This obviously just checks that the input is able to be converted to an image. However, it should show you as a use-case how you can leverage Intervention and any of it's methods to create a custom rule.

You can extend the Validator class of Laravel.

Laravel Doc

But anyway try this

Validator::extend('is_png',function($attribute, $value, $params, $validator) {
    $image = base64_decode($value);
    $f = finfo_open();
    $result = finfo_buffer($f, $image, FILEINFO_MIME_TYPE);
    return $result == 'image/png';
});

Don't forget the rules:

$rules = array(
   'image' => 'is_png'
);