It depends on the route you want to go. Some people say a guitar teacher is necessary... I would say not. Plenty of the most well known guitar players in the world on not trained by a teacher.
Think about the music you want to play.
Almost anything in the blues/rock world can be self-taught. There is not a right way to play the blues, no matter what the elitists tell you. And rock (sometimes) is a natural extension of blues.
Now if you want to break into classical or metal, you will need to learn some classical techniques. Know your scales, chords, and how to improvise in a technical setting. There are, however, parts of the metal world where unconventional playing is welcome, and even encouraged. Such as funk metal.
My advice is this:
If you plan to go into a technical music genre, get yourself a teacher and learn to do things the "right" way, so that you can play with others freely when you get good enough.
If you want to play by yourself, or are going to stick to less classically influenced music types, just head over to youtube!
I learned guitar for about 3 years on nothing but youtube videos and a chord book. There was a particular guitar player that I admired at the time and I just watched live videos of him and imitated what I saw. Overtime, I became proficient with the guitar and started writing my own songs. I believe this is a very creative and enjoyable route if you're willing to not be taken seriously by more technical bands and guitarists.
Regardless of what you choose. Make sure you spend time learning the songs you love as early as possible. Nothing kills the learning motivation like playing stuff that does not interest you.