So then I toddled over to read the contest rules and found this gem:
License to Use Entries: By submitting an Entry, each entrant agrees and hereby grants to Sponsor and its successors, licensees and assigns an unlimited, perpetual, irrevocable, assignable, royalty-free, fully paid-up license to reproduce, distribute, perform, create derivative works of, edit, alter, display, exhibit, combine with other materials, exploit and otherwise use the Entry, and all elements embodied therein, in any manner and in any and all media now known or hereafter devised throughout the universe for any purpose whatsoever, without compensation or notification to, or permission from, entrant or any third party and hereby waives any moral rights in the Entry.
My picture is my picture. My dog is my dog. Why should I release rights in perpetuity for something I've created of something I love a great deal to somebody to do what they want with it? I understand that, in general, rights like these are so they can make those creepy "dog with human teeth" advertisements. But seriously, even if you don't win, even if you just enter, you are giving these rights to Dentastix (and Pedigree, by extension, it would seem) and its successors royalty free and across the universe however they want for ever and ever amen. And they're not responsible for third-party usage of submitted entries. And you're not allowed to watermark them, because identifying information, yadda yadda.
In my Why I Watermark my Pictures post, "protection against misrepresentation" was one of the reasons I gave. I would be just sick if a contest entry of mine, given in good faith, became a stock image for Dentastix/Pedigree/whoever to trot out any time they wanted a vicious or dangerous dog picture, or even to just advertise a product I dislike and wouldn't support. Maybe I'm paranoid, maybe I'm thinking too much about it, whatever.