Wireless Image Sensor Networks (WISNs) consisting of untethered camera nodes and sensors may be deployed in a variety of unattended and possibly hostile environments to obtain surveillance data. In such settings, the WISN nodes must perform reliable event acquisition to limit the energy, computation and delay drains associated with forwarding large volumes of image data wirelessly to a sink node. In this work we investigate the event acquisition properties of WISNs that employ various techniques at the camera nodes to distinguish between event and non-event frames in uncertain environments that may include attacks. These techniques include lightweight image processing, decisions from n sensors with/without cluster head fault and attack detection, and a combination approach relying on both lightweight image processing and sensor decisions. We analyze the relative merits and limitations of each approach in terms of the resulting probability of event detection and false alarm in the face of occasional errors, attacks and stealthy attacks.