So, for many species a lower number may be required. The optimal number is determined by the size of the area and the visual variation in this area. If there is not much variation, a lower number is more appropriate. Remember, the software will always find the number of requested key points, and if there is not much variation, a significant part of the key points may not be meaningful if the key point number is too high. The optimal setting is best determined with an experiment with 30-40 individuals and 2-3 photos per individual.