2008 Toyota Tacoma 4x4 Oil Leak

First off, forgive me guys, I'm not an expert by any means on engine work. I noticed a small spot of oil on my driveway today (about the size of a dollar bill), and have since located a small leak underneath my truck. It appears to me that it could be the oil pan seal. After drying up all the oil, I then noticed the highest spot from which I saw oil, with looks like a threaded spot for a bolt, above the oil pan. I don't know if there's suppose to be a bolt in there or not. Here are all the pictures I took. Any help would be greatly appreciated.

 

Definitely looks like there should be a bolt there. Can you get a wider shot of that missing bolt?