What are my options to get a defined jaw line? (Photo)

You would benefit from mandibular and/or chin implants to improve the definition of your jawline.  Depending on the neck tissue thickness on examination some jawline liposuction may help as well.  Hope this helps.  As always, best to see a plastic surgeon for a formal assessment to determine your ideal options.

While I cannot give you specific suggestions just based off the one photo, there are several things that you can consider. I actually get this question quite often. The easiest way to get the results you want is by using hyaluronic acid fillers. Several syringes may be needed, but I have had some very good results with it. The downside is that it's not permanent. 
Another option is to put in a silicone implant through an incision in the mouth. I would recommend doing this under anesthesia since it is a tough area to get to in the office, although not impossible. It is a fairly quick procedure, and there are a number of different shapes and sizes of implants that can be tailored to you. I often will do custom carving of the implant in the operating room so that the shape perfectly matches your goals. 
I hope this helps,
Sarah Saxon, MD

Tara,
In order to provide the sharp lines that Angelina Jolie has you need a few things. First, you need to be thin. Second, you need to have tight skin. Third, you need the bone structure. It appears you have the thin-ness and skin necessary to get the result but need some help with your bone structure. It is hard to tell everything from a single profile picture, but a combination of chin implant and mandibular angle implants (placed at the lower back of the jaw bone) I think would give you the jaw definition you are looking for. Try to find someone skilled in bony reconstruction of the jaw, generally a craniofacial surgeon that does cosmetic work.

Good luck!

The jawline can be viewed at various angles as you note and the 45 degree is the most appropriate for your concern. Typically it is the actual width of the lower jaw which is important since it separates the face from the neck. Augmentation along the length of the jawline is commonly performed to achieve your goals (see website) and is readily performed intraorally. The definition is very impressive when balanced with the midface too.