Any strategy for detecting faces in an image, for example, cannot be expected to detect airplanes as well. Just like a person, a computer needs different strategies to detect different objects. As a machine explores its environment in the context of a task it gathers exploitable knowledge about which actions lead to success. The specific knowledge depends on the task, but the learning method is task-independent. Machine learning allows strategies tailored to a particular data set to be developed without any simplifying assumptions.
Machine learning can provide general solutions a task-specific problem like object detection.
Detecting faces in cluttered scenes. The algorithm could be applied to any other object detection problem without modification. Only one scale is trained. A large set of faces and non-faces is trained in hopes of discovering a general solution. Applicable to face detection, but the entire scene must be searched through scale space.