Monte Carlo photos employ a rendering technique called Monte Carlo path tracing to simulate the physics of light in 3D scenes. This technique involves randomly tracing paths of photons through the scene, simulating their interactions with objects and surfaces. By leveraging statistical sampling and algorithms like Metropolis-Hastings and MCMC, Monte Carlo path tracing generates photorealistic images with accurate lighting, shadows, and materials, enhancing realism in fields such as architecture, product design, and visual effects.