Jimmy looks at a picture of a side of a submarine that has dents and bumps on it. When he turns the picture upside-down, what he originally perceived as bumps, now look like dents, and vice versa. This is due to

This is due to light from above heuristic.

Explanation:

In light from above heuristic, they we perceive spheres and indention are altered. Our eyes are so much used to of sunlight, that we assume that the light is coming from above and creating a presumption that light on the bottom creates an indention.

This is why Jimmy perceived bumps originally when he looked the picture of the side of the submarine but later when he turned the picture upside down, what he originally perceived as bumps, now look like dents,