I don't know what the original program would have been. You would have found that information in your file associations list. On your computer, you won't be able to find that information anymore since the installation of Photo editor will have reassigned your file associations.
If you can find another computer that opens .jpg's the same way yours used to, you can check the file associations on it. Once you know what application it is, you can load that application on your computer. This should reassign the file associations to the new application.