You can win two of the three categories in one of these combinations:
1) Win "Top Photographer" & "Guru's Top Pick"
2) Win "Top Photo" & "Guru's Top Pick"
This is done to avoid cases where a single member 'sweeps' all the prizes (since "Top Photographer" usually has the photo with most votes).
Secondly, the "Guru's Top Pick" is done by using the same voting system as the users so they don't know who they are picking.
* Winners can only receive one prize bundle per challenge. This means that if you rank in the Top 50 category in addition to winning the challenge (as Top Photo, Top Photographer, or Guru's Top Pick), you will not be eligible for the Top 50 prize or achievement.