The power of crowds – leveraging a large number of human contributors and the capabilities of human computation – has enormous potential to address key challenges in the area of multimedia research. Crowdsourcing offers a time- and resource-efficient method for collecting large volumes of input for system design and evaluation, making it possible to optimize multimedia systems more rapidly and to address human factors more effectively. At present, crowdsourcing remains notoriously difficult to exploit effectively in multimedia settings: the challenge arises from the fact that a community of users or workers is a complex and dynamic system highly sensitive to changes in the form and the parameterization of their activities.