If you are competitive in nature, then you have probably already entered a render contest or two. Besides being fun, they can also be educational for a newer render artist. Even those not so new can benefit. There are lots of different render contests. Some may be specific for software, others may require certain products to be used in the image, or others may have a theme such as a new movie. For many artists, having criteria for creating an image helps give them some direction but allows for some great interpretations for the final images by artists. This can be educational as it gives you an opportunity to see what other artists do with the same items and compare your work.
Some contests are run weekly, others monthly and some only once or twice a year. Keep an eye on the forums as new contests are often posted in them. The judging at any artistic competition is subjective as most of the judges are artists and will be more inclined to award the art the genre or a type similar to their work, so that should be taken into consideration before submitting entries. In other words, if you enter a contest where the judges are heavily into portrait work and you do landscapes, don't expect to win. Some judges are willing to look at all types of work, but not all. And like any other competition, don't be surprised to see the same names win. Often they are just that good, so study their work to see where you can improve your own. Prizes usually vary from gift certificates or software at the website store where the contest is being held. The following is a list of some of the render contests that are run at different sites:
Beginners
DAZ3D runs a New User contest monthly at http://www.daz3d.com/forums/categories/new-user-contests-and-events
There is a WIP component where your work is critiqued by experienced users to help you improve the image before entering it.
Average to Experienced Users
OK I'll start with my favourite contest which is Shiba Shake's monthly Vendor Awesomeness contest. This contest is run monthly and items from specified vendors must be included in the image. Any software can be used. Entries are uploaded to the DAZ3D galleries to be entered. For entry details visit Shiba's website at http://thinkdrawart.com/3d-art-contest
While you on her site I recommend that you look at the past winners in the contest as Shiba also includes critiques which can be a great learning experience.
If you are a member of DAZ's Platinum Club then there is a weekly competition which requires you use the latest PC items in the image. They also have a monthly challenge based on a theme. For entry details visit the DAZ Platinum Club Members Only forum. You will need to be a PC member to see this forum. Both Renderosity and Hivewire run contests through the year. Hivewire contests require the use of certain items from their store. Popular challenges are the Ken Gilliland "Bird" or CWRW Hivewire Horse annual contests.
Cornucopia3D.com/E-on Software hold the occasional render challenge but this would be for Vue users only. Usually based on a theme their latest contest was for The Jungle Book movie.
Experienced 3D Artists
CGSociety.org often has render challenges but these are for experienced 3D artists with extremely high quality images being entered.
There are lots more 3D contests out there and this is just a short list. If you know of other contests please post them in the comments.
BTW check out my post The Golden Years for 3D characters for a contest currently being run during September 2016 with some decent prizes.
Happy Renderings!