How to run a photo contest privately and online ?

I am running a small photography group with about 25 members who are interest to learn and improve their photography skills. Our team plans a outing every weekend and do photography. So every week we do a contest. Now we are taking print out on the spot voting system. But still many or not convinced or looking for still a better option in the voting technic. For me also every week taking print out in color laser print also cost me a lot.

Is there any sort of app or webpage, where we can run the contest within the group alone instead of public participation. We have created our webpage using the NING platform.