Good question! Here is answer:
► If there is folder of your series name, put the picture there.
► If there is no folder with your series name, put it another folder. Is your cosplay in anime, manga, movie, videogames, disney or western comic? There is folders for those.
► If you costume is not cosplay, you can put it in own non-cosplay costumes folder. You can put there all other costumes which aren't really cosplays. (like random elfs, orcs, witchs etc.)
► If you photo is nudity, violence or K-18, put is on K-18 folder. Always.
► If you photo is collage how to do something, put it in tutorials.
► Yaoi / yuri folder is under K-18 photos. If you have K-18 yaoi or yuri picture, put it in K-18 Folder.
All folders (except K-18) are under K-18 folders. So no violence, nudity or sexual themes on those!
You can always suggest a new folder. Sometimes we hear your suggest and create a new folders, sometimes we don't.