Contest Question

I am running a contest (for fun) at this moment and I have noticed something that I have seen before. it doesn't make sense so I thought maybe one of you might know the answer to my question. I am only allowing one image per member so one would think that if you have 100 images that you should have 100 members. However more than one when I allow only one image in any contest that I am running the numbers for images do not match the number of members. I should also note that only FAA members can enter.
You can can find the contest overview at the link below. As of today there were 353 Members and 355 Pieces of Artwork. How can that be?

http://fineartamerica.com/contests/1-sunrise-sunset.html?tab=overview