Its not required but it is a good idea to take two photos incase there was a problem with the original two you submitted. As JohnnyCash had suggested and there have been atleast two cases that I have seen on this Board, the I/O may ask for pictures (for instance if they have been misplaced by USCIS). In one case instace the applicant had the pictures with him and the case was 'recommended for approval' right there, in the other case, both husband and wife had to go and get their two sets of pictures from outside and only then they were recommeded for approval.
There is a low probablity that it will happen to you, once again pictures are not required during the interivew, but if I were you, I would not take a chance... its totally your call.
Good luck.
