This paper introduces a novel "HoLiSTiC" framework for visual sensor networks (VisSNs) and studies security issues within this context. The HoLiSTiC paradigm, which encompasses many existing VisSN proposals, effectively exploits heterogeneous wireless sensing and communications for more flexible, practical and scalable visual surveillance. Security aspects of HoLiSTiC are considered by highlighting open research problems. Secure routing issues in unidirectional optical free-space sensor networks that form the foundation of the HoLiSTiC transport network are discussed. In addition, a novel distributed security paradigm based on independent media sharing is presented to demonstrate how the interaction of signal processing, networking, and cryptography can benefit VisSNs.