I forgot to replace the Cocos2D default iTunesArtwork file with a proper one. But when I tried browsing my app page, in iTunes app and website, it doesn't seem to use this file anywhere. So I don't know if I should be worrying about having this wrong file or not since I don't know where it will appear.
In this Technical Q&A page, it says that iTunesArtwork is used in Ad Hoc iTunes. But where is that?
iTunesArtwork is the file that is used by iTunesConnect when displaying your app's logo on the store.
It's optional, and most people choose to keep their bundle sizes small and just upload the artwork to iTunesDirectly rather than adding it to their app.
The format and sizes for this and other icons are described in A Developer Q&A 1686