When the students went out for a group photo, there happened to be a bug on the camera lens, so why didn't there be an image of the bug in the photo?

First of all, the principle of the camera is to make the object show an inverted image within the focal length of 1 to 2 times through the zoom lens (convex lens). Through a series of complicated transformations, the optical signal is converted into a digital signal and stored in the memory card. Then the bug on the lens, the distance must be less than 1 times the focal length, so it will not be imaged. People are dark because insects don't image, but they block the light, so they are dark.