Typically in any competition the organisers and supporting partners will claim the right to free use of submitted works in order to promote the competition.
Organisers/sponsors need those rights and The Bill of Rights for Artists permits this free usage subject to certain conditions. One of those conditions is that you are always credited on each occasion any work you submitted is used to promote the contest.
Being credited is an extremely important moral right. It ensures you are rightfully acknowledged as the creator of your work. It informs others who to contact should they wish to purchase a license from you to use it.
Contests which do not have a statement clearly stating that credits will always be given when works are published or exhibited should not be entered.
If you would like to know more about copyright and related rights please read our Guide to Rights and Licensing.