Using act as votable

I am fairly new to RoR and I am working on a project that is a picture contest. The user will post several pictures and then everyone will be able to vote for the their favorite picture. I have several models at play. The contest model which is a grouping of pictures. The pictures model which belongs to both user and contest. And user model which can vote. I need users to be able to vote once for their favorite picture in a contest, essentially picking it as their choice. I am trying to use act_as_votable to accomplish this? Would this be done using the scope? Is there a better way? Any help/code examples would be greatly appreciated.