I set up the screen saver to a folder containing some of my photos.
How do I get the screen saver in Mavericks to display them full screen?
Go to System Preferences → Desktop & Screen Saver and choose the Classic screen saver:
Since the Classic mode might not show full screen (depending on original size)
I would use the:
Ken Burns Option in the settings.
Go to System Preferences → Desktop & Screen Saver and choose Ken Burns mode.
There is some animation going in that mode but it is rather pleasing.