Vision sensors based upon pixel-parallel cellular processor arrays offer the unique opportunity to realise high-performance, flexible, low power image processing systems. By virtue of processing on the focal-plane, the energy-demanding requirement to digitize a captured frame's raw pixel data is reduced, with returned data constituting only that which is salient. We describe a stand-alone vision system incorporating a SCAMP-3 vision chip, an FPGA and an ARM Cortex-M3 microcontroller. SCAMP integrated circuits operate as SIMD computers; each pixel incorporating a compact but powerful analogue processor and local memory, with all operations occurring in parallel over the 128 × 128 array. Algorithms are developed to operate natively upon the focal-plane as far as possible, with additional serial and higher-level operations occurring on the microcontroller. The power consumption of the system is algorithm-dependent. An algorithm developed for loiterer detection at 8 fps has been shown to consume an average power of 5.5 mW, with a more complex object tracking and counting system consuming 29 mW.