> Is there a charge for the online version if I own the PC version.
No, there is no any payment for usage of the online version.
> Also can I migrate both the data and image files to the online version
This functionality is in development right now. We hope it will be ready in CS version 3.61, where one way connection (CS -> online CS) will be ready. Later we will develop backward connection (online CS <- CS). Currently you can use CS online in mode when you manually add new collectibles.