I can't be 100% sure about this event open for international, but the information and rules included in English language for the first time at the Kotobukiya official website so it is possible anyone who had Frame Arms Girl model kit can participate.
You can find out more at official website and can start submitting photos (follow the rules) of your work today until closing on 4th January 2016. The award are definitely attractive!
Update#1: Send them email, but no response. <=\