Rate each image on a scale of 1 (very unrealistic) to 5 (indistinguishable from real). Focus on: artifact presence, lighting consistency, object coherence, and overall plausibility. Use keyboard 1-5 then Enter.
Take your time with each image. There is no time limit. Your response time is recorded for analysis but does not affect the study. Try to be consistent in your ratings. If unsure, go with your first impression.