Final answer:
When using an object in front of a terrestrial background, caution should be taken when the object is closer to the observer than the background.
Step-by-step explanation:
When using an object located in front of a terrestrial background, caution should be taken when the object is closer to the point of observation than it is to the terrestrial background. This is because the object may appear larger and more prominent in relation to the background, which can distort the perception of its size and position. The phenomenon responsible for this is called parallax, which occurs when the observer's viewing position changes.