class SomeArchetypeWithImages(...):
    def __bobo_traverse__(self, REQUEST, name):
        if name in self.image_field_ids:
            field = self.getField(name)
            image = field.getScale(self)
        else:
            # decode request
            parts = name.split('_')
            field_name = '_'.join(parts[:-1])
            scale = len(parts) > 1 and parts[-1] or None

            if field_name in self.image_field_ids:
                field = self.getField(field_name)
                image = field.getScale(self, scale=scale)

                if scale in field.sizes and not image:
                    try:
                        state = self._p_changed
                    except (ConflictError, KeyboardInterrupt):
                        raise
                    except:
                        state = 0

                    # as unrestricted user ...
                    old = security.loginAsUnrestrictedUser()
                    try:
                        # recreate (all!) scales
                        logging.warn(
                            'Recreating scales for: %s.' % \
                            self.absolute_url(1))
                        field.removeScales(self)
                        field.createScales(self)
                    finally:
                        security.loginAsUser(old)

                    if state is None:
                        self._p_deactivate()

                    # try again
                    image = field.getScale(self, scale=scale)

            else:
                image = None

        if image is not None and not isinstance(image, basestring):
            return image

        return folder.ATFolder.__bobo_traverse__(self, REQUEST, name)