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I pay $10 a mo/ for 1TB of Google Drive storage and this works great. Note, as pointed out by this will count against your Google Drive storage whereas if you just stored them in Google Photos, you can make use of the unlimited storage.
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First you have to install the Google Photos Uploader for OS X.Once it's setup, the sync is done for you. It requires a few different steps to get it set up though.
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You can automatically download your photos from Google Photos (I believe Google+ photos end up there, correct me if I'm wrong) fairly easily.
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