According to one aspect of the teachings presented herein, a machine vision system includes one or more sensor units that are each advantageously configured to use different pairings among a set of spaced-apart image sensors, to provide redundant object detection for a primary monitoring zone, while simultaneously providing for the detection of objects that may shadow the primary monitoring zone. Further, a plurality of “mitigations” and enhancements provide safety-of-design and robust operation. Such mitigations and enhancements include, for example, bad-pixel detection and mapping, cluster-based pixel processing for improved object detection, test-image injection for fault detection, dual-channel, redundant processing for safety-critical object detection, temporal filtering to reduce false detections, and the use of high dynamic range (HDR) images, for improved operation over variable ambient lighting conditions.