Optically driven photoconductive switches are one of the predominant sources currently used in terahertz imaging systems. However, owing to their low average powers, only raster-based images can be taken, resulting in slow acquisition. In this work, we show that by placing a photoconductive switch within a cavity, we are able to generate absolute average THz powers of 181 μW with the frequency of the THz emission centered at 1.5 THz—specifications ideally adapted to applications such as non-destructive imaging. The cavity is based on a metal–insulator–metal structure that permits an enhancement of the average power by almost 1 order of magnitude compared to a standard structure, while conserving a broadband spectral response. We demonstrate proof-of-principle real-time imaging using this source, with the broadband spectrum permitting to eliminate strong diffraction artifacts.