Does my own profile picture affect face detection?
Good question, but no. Only the pictures you've uploaded into your library affect the way Ponga adds names to faces.
Adding your own profile picture to your account is a nice way to give the people you share your pictures with a visual reminder of who you are. They might remember you as a guest at a wedding but not quite have remembered your name.
The picture you add to your profile is completely separate from the pictures in your Ponga library, however. Once you add a name to a face in the Gallery, Ponga will look to connect that name to every other instance of that person's face as they appear in pictures in your account. Remember, it only automatically applies the name when it can be sure they're the same person with a high degree of confidence. Otherwise, the faces that appear in new pictures will be added to your Gallery for your individual review.
Learn more about your account settings panel in How to manage your account.