In our master course we offer a project on pervasive advertisement (it is an interdisciplinary course project from computer science and marketing) where we look at future forms of advertisement that become possible by new technologies.
The students presented a set of really exciting ideas - an I would expect (if they get some of their ideas implemented) that advertising will be more entertaining and fun in the future. For some of the ideas we discussed potential privacy issues and I promised to provide later the reference to the German privacy law that restricts the use of optical/camera devices in public spaces. The German law is at a first glance very restrictive with regard to using cameras in public spaces. In short it can be summarized that data can only obtained for a legitimate, concrete and defined purpose and that the privacy interest of the people are not higher to value as the purpose. Additionally it has to be clear to the person observed that he or she is observed. (We probably need a lawyer to figure out what is allowed ;-) In  the text of the law (in German) can be found.
 Bundesdatenschutzgesetz. § 6b Beobachtung öffentlich zugänglicher Räume mit optisch-elektronischen Einrichtungen