How to defeat a paired picture based password?

How to defeat a paired picture based password?

If a system has a set of 40 pictures and each user select 20 pictures as
their favorite pictures for password authentication.
The system will authenticate a user as follow: present 2 pictures and the
user will select the one that is from his favorite pictures. The system
will repeat the process 20 times, hence 40 pictures.
If the user has selected their 20 picture successfully from the 20-pair
sets, they will be logged in.
What is the search space for an attacker to crack the system and log in as
a user?
Here is my try:
I thought that the attacker will use a program and brute force as much as
2^20 times.
Is this system more secure than a standard password authentication system?