The number of craters a kilometer or more in diameter is the same in both pictures. The explanation is that most small craters can be recognized as such only by the shadows they cast. The materials on their walls and rims are commonly indistinguishable from those of the surrounding terrain. For each picture there is, depending on the angle of Sun elevation, a threshold value of slope below which no shadow is cast. An observation immediately follows.
Small craters have a relatively short lifespan.
That is, once formed, they are rapidly degraded. Their rims are eroded, and their interiors are filled with debris from the continuing bombardment of the surface by other impacting bodies. It is fruitless, therefore, to count small craters because such counts will result in the same false age. Fortunately, the crater counting method does yield satisfactory results when applied to larger craters. The same number of craters larger than about 1 km is visible in both pictures.