User-created challenges have been designed to inspire your creative process and help build a sense of community. There is no prize or trophy associated with these challenges. Users receive points towards their status each time they participate in a challenge.
How about the trophies I see in some user's profiles?
Trophies are assigned only for official challenges that are created by ShopLook (you can find these by looking for the official icon on the challenge). If you are selected a winner, you will receive a trophy on your profile page that will be visible to other users.