No idea is my answer, although it seems that when a new DLC is released, there is an influx of Editors Picks of pictures which feature that DLC. Otherwise, they just seem like "out of the ordinary" photos to fill the gap. There's some really good photos on the editors picks that make you go 'Wow, how?!' but there's also some terrible ones that make you go 'Um, this guy got picked?' - There doesn't seem to be any consistency with regards to the quality of the photos.
Also, the Most Viewed and Best Rated are getting extremely boring. It would be nice to see a rotation like 'Most Viewed this month' or 'Best Rated this month' etc.
But to answer your question, I don't know how to get picked