As I understand, there's no official G+ API for getting photos from albums. But I've figured out from here that Google Plus uses Picasa internally.
My questions are:
Thanks in advance.
The link you "figured it out from" tells what you need to know. That first big number in the page URL is the UserID. From there you can call something like:
https://picasaweb.google.com/data/feed/api/user/115999964287637644901
and it will give you a list of the albums available. Drill down from there.
Downside? Sometime soon Google is no doubt going to change all this by implementing a real G+ API for photos.