Is there any way to automatically download or sync all photos backed up from my phone to Google+ to my Mac?
I know there is an upload tool, but I want the reverse.
Can they be viewed from Picasa somehow?
You can automatically download your photos from Google Photos (I believe Google+ photos end up there, correct me if I'm wrong) fairly easily. It requires a few different steps to get it set up though. Once it's setup, the sync is done for you.
Google Photosoption. Ensure the settings pane for Google Photos on Google Drive has the Create Google Photos folder enabled.
At this point, your photos will sync from your mobile device and desktop to Google Photos, be linked to Google Drive, and sync back down to your desktop for you to pull in to what ever app you want.
Note, as pointed out by @Jer, 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. I pay $10 a mo/ for 1TB of Google Drive storage and this works great. I organize all my photos into subdirectories, tag them and manage them via Adobe Lightroom, with Google Drive automatically syncing them to Google Photos on my phone. It also lets me easily select a folder I've organized via Lightroom and share it with other people via Google Drive, instead of having to build out albums and share via Photos.
You can download all Google+ photos in one go using Google Takeout.
The solution by Johnathon Sullinger has caused photos to sync using Google Drive, which counts towards your 15GB limit. Ended up having to delete and re-upload using photos. So sync cannot work both ways without counting towards drive storage limits as far as I can tell.
Also, at this point in time, Google Photos only end up there if you give permissions from both accounts, which you wouldn't want unless you're only uploading from Google Photos.
Here are the facts... it IS bi-directional, and it does NOT count against your Google Drive storage if you are syncing to/from Google Photos and not simply uploading photos into a random folder.
If I take a picture on my camera, it automatically uploads to Google photos once I'm on wifi. It automatically shows up in my "Google Photos" folder on Drive, AND it shows in my offline Google Drive's "Google Photos" folder on my Mac.
If I drag a photo into my offline Google Drive "Google Photos" folder on my Mac, it automatically uploads to sync with my Google Drive "Google Photos" folder in the cloud, and it shows up in Google Photos online.
And my Google Drive shows that I've used "5.2 GB of 15 GB" allotted storage, but my Google Photos folder contains about 86GB (yes, eighty-six).
If you set it up right, this is how it works.
I just did this:
FIRST, create a folder on your desktop and name it (mine is "G+ Pix"). You will need this folder for step #5.
1) Open Google+ Photos to see your list of pix. Select the group of pictures you want to export by clicking on the check mark in the upper left hand corner of the pic. Using the "shift" key on your keyboard helps you do multiple selections at one time. These pix will remain in G+, because you are downloading copies of the pix. I selected by date in order to keep the download times manageable. It was easier to keep track of what I had selected, also. I had 900 pix to move!!!
2) Select the download button found with an underscored arrow at top right of the Google+ menu bar.
3) You will see this group of photos being downloaded as "Photos.zip" in your download menu at the top right of your MAC screen.
4) When download is complete, the file will read "Photos" with a blue folder to the left of it. This downloading process can take awhile, depending on the number of pix you export and the level of picture quality you determined when sending pix to G+, initially.
5) Double-click this file and your pix will appear in list form. Highlight this entire list by using the "shift" key on your keyboard for multiple selections, and move the list to your designated folder on your desktop. From this desktop folder, you can now manipulate them as your please.
Multiple Selection Tip
Select first picture
Hold down "Shift" key as you selected last picture.
All items should now be blue and will transfer as one group by holding down the curser on the list as you slide them to the desktop folder.
Anyway, this worked perfectly for me. You have to play the game, man! Ugh!
Google has purposely blocked this by not releasing bio direction sync on any platform even the phones wont sync downloads they just show up in the viewer and you have to select them to download a copy to your phone. Google photos is for auto upload only not auto download. Until people demand this service and another vendor provides it google will never allow it.
The other solution is to install a android emulator, install google photos and click on the photos you want to download. Not sure if a emu exists on the mac tho.
Google+ Auto Backup for MAC. I have been running it on my MAC with current OS and it works well.