Sometimes, problems in an animation or track are only apparent when the image is moving, which is why artists tend to scrub, flip, and loop their work. Similarly, differences between two images are more apparent when you “A/B” them – toggle quickly between them several times with each image registered exactly on top of the other.
Ambient haze (atmospheric perspective), shadow tapering, and depth of field of some visual cues that help sell an image as looking photographic/realistic.