Is it possible to root a phone without knowing a the phone's pattern/pin/password? This question isn't because I need to root a phone without a pattern/pin/password but because I was curious and thinking about the process. I'm assuming that you would have to put the image on an external SD card and then load it from there.
Short answer: Yes, it is possible. Different techniques can be used for this purpose (some of them are described e.g. in Andrew Hoog's book Android Forensics: Investigation, Analysis and Mobile Security for Google Android). It especially gets easy when USB Debugging is turned on.
Long answer: Please forgive me if I don't give this. Just a hint: There are exploits, and there are custom recovery images...