I don't enter photo contests anymore, half of the time the judging is fixed. I entered a photography contest put on by a local magazine and they were giving away a $800 camera for first place and second place a Leica p&s camera and for third a Manfrotto tripod and on top of that your photo is on the cover. Pretty good prizes right?
The contest was farming and so I entered the perfect picture, spent time and money finding the right location. When the winner was announced I was disappointed because the winner had one of the worse photos that had been entered, it was taken with a phone, it was washed out, horizons wasn't straight..just looked like he pulled over on the side of the road and took a snapshot and won. Did some research on this guy and found out he works for the magazine. No wonder why he won. The people who won second and third place were never mentioned.
Also entered one where I didn't win, but they used my photo anyways. You just need to be careful, do some research and read their terms and conditions and then make an informed decision.
I'm sure some contests out there are 100% legit and not bias. I prefer contest where public votes instead of judges. But I don't bother entering them anymore, I just enjoy shooting.