Nerd Pig has glasses, red back pack, and a pencil in his tail!
Instructions: (I highly recommend you copying the original pig.png file and saving it some where you can find it easily)

- Go to your .minecraft folder (you can locate it by typing %appdata% in the address bar).

-After you're in your .minecraft folder, open your "bin" folder. Then locate your "minecraft" section and open it with 7-zip or anything that will open you to its archives.

-Then scroll down to the folder "mob" and open it. Find "pig.png" and delete it, then replace it with this pig.png I'm sending you (located in the "mob" folder in the download). (this is why I highly recommend you copy the original "pig.png", so you can put it back to normal if you want.)

If you have ANY problems, just let me know and I'll help anyway I can :)