check website each year
US Residents - see the Official Rules
These vary according to the theme. For example, the portrait contest offered a Nikkor 85 mm f1.4 lens, perfect for portraits.
Website: Nikon Inspirations
You can have a look at what other photographers have submitted so far and previous winning images. There are lots of extraordinary photographs to provide you with inspiration.
Take note of the Official Rules, particularly Point 7 which explains which rights you'll be granting to Nikon when it comes to using your photograph if you win.