An analogy for a CCD device is a football completely field filled with a grid of paint buckets. The photons of light are like tennis balls dropping into these buckets. As more balls fall into certain buckets their light value goes up. Sometimes the balls may bounce out and lind in an adjacent bucket. On a CCD camera, as the chip get hotter, more balls bounce into other buckets. This can result in dots in the image whre they are not supposed to be.

An CCD camera for astrophotography has a cooling device that helps keep the light where is is supposed to be.