Kick boxing or something similar could be a good idea to help weight loss. It will get you fit and - crucially - if you like it, it will keep you motiviated as you start to intergrate with a new group of friends.
The picture you posted isn't working, so don't know how big you are but I dont think it would matter too much. They aren't going to throw you in a pro-ring on the first day. Kick Boxing is very cardio intensive, so you will get tired regardless of your size - and you'll also get fitter.
Any of the martial arts are good for this kind of thing though. Its a great way to loose weight and meet new people - if you stick at it. At the martial arts clubs that I attend there are people of all different shapes and sizes - and everyone gets a good workout. Afterall, you only work to your own limitations - not everyone elses.
The gym is also a good idea. They have personal trainers who can assist you in reaching your goals. However, if you don't fancy a gym, try mags such as Mens Health which give tons of practicle advice on training and eating. Walking, swimming, jogging or sports (racket sports are great fun and excellent workout) are also simple, cheap and an excellent start.
Whatever you choose, remember to keep it regular.
Good look, and enjoy it! If you don't enjoy it, try something else. Thats they key.
