Is there a way to automatically upload photos from an iPhone to Google Drive

You should use the app Photosync which let you choose where to download your pictures, including Dropbox, Google+/Picasa, Box, 500Px and Google Drive (!) to answer your question.

Use Google+! Switch on auto back up, check settings to make sure it uploads over wifi only perhaps.

Also, the Google+ app offers the option to upload full-size photo files, which will use your Google Drive space allotment, or to upload unlimited "standard-sized" photo files. Standard size means they are resized to 2048 on the longest edge. This is a nice option if your photos are mostly snapshots or mostly just viewed on screen and never printed.

Yes, Google Drive has a built-in option for automatic photo backups.

Go to Settings -> Photos and enable Auto-Backup. If you choose to upload in High Quality instead of Original, the uploaded photos won't count against your Google Drive storage limit.