How do I rewire this ceiling fan?
TL;DR: Whoever installed your ceiling fan had some terminal screws loose

The good news is that the green wire is unmistakably tagged as an equipment grounding conductor, and was likely not the current return path in the original  wiring configuration.  The bad news is that whoever originally wired this did a hack job, deciding to use some blue wire they had left over from the last hack job as a neutral wire (grounded conductor), which grossly violates NEC 200.6(A):


  200.6 Means of Identifying Grounded Conductors.
  
  (A) Sizes 6 AWG or Smaller. An insulated grounded conductor of 6 AWG or 
  smaller shall be identified by one of the following means:
  
  (1) A continuous white outer finish.
  
  (2) A continuous gray outer finish.
  
  (3) Three continuous white or gray stripes along the conductor's entire length 
  on other than green insulation.


Now that that facepalm moment is out of the way, it's possible to fix this by nutting the blue and black conductors from the fan to the black wire from the ceiling, and the white wire from the fan to the blue wire from the ceiling.  While you're up there, please, please, please tag the blue wire from the ceiling with a piece of white electrical tape -- there's no way to bring the current situation fully up to Code without ripping out the offending neutral wire and replacing it with a white or grey wire, but a tag will at least keep the next electrician's eyeballs from frying when he or she stares at your ceiling fan's wiring.