With the increasing popularity of digital multimedia such as images and videos and the advent of the cloud computing paradigm, a fast growing amount of private and sensitive multimedia data are being stored and managed over the network cloud. To provide enhanced security and privacy protection beyond traditional access control techniques, privacy preserving multimedia retrieval techniques have been proposed recently to allow content-based multimedia retrieval directly over encrypted databases and achieve accurate retrieval comparable to conventional retrieval schemes. In this paper, we introduce a security definition for the privacy preserving retrieval scenario and show that the recently proposed schemes are secure under the proposed security definition.