Security scanning devices based on electrical tomography, including tomography systems based on the measurement of capacitance (ECT) and electromagnetic tomography (EMT), in combination with knowledge-based image analysis and understanding. Each device includes a sensing head or transducer, sensing electronics, image reconstruction and image analysis microprocessor, a display unit and accompanying software for identifying dangerous materials and items. The security scanning devices are employed for obtaining multiple independent measurements and enable implementation of data fusion to combine the complementary sensitivity of ECT and EMT to different material properties, while providing architecture to implement image knowledge bases, which characterize objects, whose image attributes are acquired from multiple sensors.