No, it's not possible to recover the images if you've already sold your phone. AppLock doesn't have cloud support, which means the remote procedure can't be used in this case. If you've uploaded the files to a cloud service, then yes, you can log-in on that website to recover the files, but remote accessing the phone is an operation not available. You can get in contact with the buyer and explain the situation. If he doesn't want to, your photos will be locked without any recovering possibility.