Photo survey tools?

I need to put together a simple photo survey for someone I am
maintaining a site for

Basically the idea is that there will be a number of photos on a page,
and site visitors will be invited to vote for their favourite. There
will be a prize of a reasonable value, so I need something with a
reasonable level of security. i.e something that is not too easy to
hack/ skew the results.

I dont really want to get involved in writing/adapting scripts etc
myself, I dont have the time or inclination toreinvent the wheel to
be honest, would prefer to use someone else's proven product.
The client is happy to pay so the solution doesn't have to be free.

I'm looking for a solution that will host the images,
survey etc on the providers own site, rather than on the one I am
looking after.

Anyone got any good suggestions, or has used something similar
themselves that you can recommend using/ avoiding? I have Googled, but
haven't found anything of much use.

Regards
Peter Jenkins
see http://www.sensiblesentencing.org.nz