The board assigns ratings to games based on their content, using judgment similar to the motion picture rating systems used in many countries, using a combination of six age-based levels intended to aid consumers in determining a game's content and suitability, along with a system of "content descriptors" which detail specific types of content present in a particular game. The ESRB maintains a code of ethics for the advertising and promotion of video games—ensuring that marketing materials for games are targeted to appropriate audiences. In , the ESRB began offering a system to automatically assign ratings for digitally-distributed games and mobile apps , which utilizes a survey answered by the product's publisher as opposed to a manual assessment by ESRB staff. Alongside its game rating operation, the ESRB also provides certification services for online privacy on websites and mobile apps. The ESRB ratings system is enforced via the voluntary leverage of the North American video game and retail industries; most stores require customers to present photo identification when purchasing games carrying the ESRB's highest age ratings, and do not stock games which have not been rated.