Computer Security Question

Alice has a picture-based password system, where she has each user pick a set of their 20 favorite pictures, say , of cats , dogs , cars , etc. to login, a user is shown a series of pictures in pairs-one on the left and one of the right. In each pair, the user has to pick the one that is in his set of favorites. if the user picks the correct 20 out of the 40 he is shown (as20 pairs), then the system logs him in. Analyze the security of this system, including the size of the search space. Is it more secure than a standard password system?