Even though many security schemes proposed for wireless sensor networks protect transmitted data content against different attacks and fulfill most of the desired security requirements, they suffer from not addressing concealing the privacy of the contextual information. Contextual information such as event incidence, event period, and event position can be exposed to an adversary by just monitoring network packet transmission. This kind of information is very important because it can leak location information of key nodes or even detected events themselves. Therefore, proposing a contextual unobservability scheme is a challenging task in sensor networks considering many issues: the broadcast nature of the wireless channel, the different attacker models, the network resource constraints, and the overhead on system performance. Most of the existing location privacy schemes are not addressing all these issues and are either not efficient against global adversaries or degrade significantly network performance. Thus, we propose in this work an innovative and effective location contextual anonymity mechanism in Wireless Multimedia Sensor Network (WMSN) that exploits the cross-layer joint design among different layers: application, routing, and MAC layers. The proposed location unobservability scheme combines the source coding technique, probabilistic packet transmission, multipath routing, and priority-based dropping policy to enhance the efficiency level of the provided privacy service without noticeably affecting the Quality of Service (QoS) requirement for delivering multimedia content in WMSN. Performance evaluation results show that our proposed privacy mechanism outperforms other proposed location privacy techniques regarding privacy efficiency (safety period) and network performance (end-to-end delay and energy consumption).