Wireless Multimedia Sensor Networks (WMSNs) are considered as one of the most prominent infrastructures for human-centric multimedia applications due to the wide availability of low-cost hardware such as microphones and CMOS cameras. By virtue of the energy limitations on sensor nodes alongside the explicit highly demanding bandwidth requirements of real-time multimedia applications, these particular networks foster a set of non-trivial challenges that need to be confronted. In this paper we define a level of relevance in regards with the content of a multimedia packet and we further introduce a dynamic routing protocol that optimizes the overall network performance in terms of energy efficiency and packet delay. We present the design, implementation and applicability of our Content Relevance Opportunistic Routing (CROR) protocol under experimental results that show an increase in network lifetime of up to 20% compared with traditional routing.