I get by with Linux but I'm by no means a guru, so please be nice :)
On my other devices (Android, Windows) I use Picasa and its Auto Backup feature to automatically resize and upload to my Google drive. Honestly, I don't really know how it works, it just works. I back up my photos full size to my Ubuntu server locally and from there to Crash Plan so this isn't about data security, it is specifically for Google+ sharing and the "neat" features they have. Because they allow unlimited photos for anything < 2048*2048 I want to resize.
So how can I:
a) resize b) upload c) stay synced
Preferably from the command line, as it is a headless server.
Oh, I should probably say this: I did just add my network folder containing all those folders into my Windows machine's Picassa... and that's working - sort of. Problem #1 is that it says its going to take 42 days to complete. The bigger problem, however, is that it is really trashing my Internet connection. I'm not sure why. I did a test with local photos and it doesn't affect my connection at all, but my VOIP was dying periodically and I narrowed it down to it being whenever the server was being accessed by Picasa for a photo. Anyway, for long term success I think I'd like to do the above rather than using Picasa for this task.