$this->validatorSchema->setPostValidator(
																						 new sfValidatorCallback(array('callback' => array($this, 'checkSize')))
																						 );

public function checkSize($validator, $values)
	{
		if(!isSet($values['logo'])) return $values;
		$maxPxSize = sfConfig::get('app_frontHal_maxPxSize');
		list($width, $height) = getimagesize($values['logo']->getTempName());
		if($width > $maxPxSize || $height > $maxPxSize)
			{
				throw new sfValidatorErrorSchema($validator, array('logo' => new sfValidatorError($validator, "Max image pixel size : $maxPxSize x $maxPxSize")));
			}
		return $values;
	}