No, you don't. But my recommendation, yes. You see, I started with YouTube then guitar magazines and online articles. But lo-and-behold, I decided to engage a teacher. I found out...I SUCK!
Yes, in the midst of playing the guitar and learning from magazines and videos. I have also unwittingly developed bad habits that I do not notice. Holding picks and such are basics, but when it comes to picking and wrist movement and how to effectively pick quickly, also chords formation and such...I realised I was far, far, far away from being a good guitarist.
So yes, I do recommend a teacher. Some people don't have a teacher, some does. I mean, Buckethead was a student of Paul Gilbert, Steve Vai was a student of Frank Zappa and Joe Satriani. Even MAB has a teacher! There are people who didn't have one and they become really good guitarists.
I'd say, get a teacher. It helps, a lot. A LOT!