gistfile1.php

<?php

class MyForm extends sfForm
{
  public function configure()
  {
    $subForm = new sfForm();
    $subValidators = array();

    $replace = new sfValidatorSchema(null, array('allow_extra_fields' => true, 'filter_extra_fields' => false));

    for ($i = 0; $i < 2; $i++)
    {
      $productPhoto = new ProductPhoto();
      $productPhoto->setProduct($this->getObject());

      $form = new ProductPhotoForm($productPhoto);
      $subValidators[$i] = $form->getValidatorSchema();
      $form->setValidatorSchema($replace);

      $subForm->embedForm($i, $form);
    }

    $this->embedForm('newPhotos', $subForm);
    $this->mergePostValidator(new MyPostValidator(array(
      'sub_validators' => new sfValidatorSchema($subValidators),
      'sub_forms'      => $subForm,
    )));
  }
}