Apparently Google+ uses a number of techniques to select the "best" pictures from the year (out of hundreds of options). It actually does a pretty good job, though I'm not sure people need to see multiple shots of a bunk bed being assembled.
Here's an example of how smart it is. Google+ chose to show this photo...
...rather than this (photobombed) one.
I guess even the robots know when they're being messed with.