I can relate to your dilemma! There are several things at hand:
1) It might be helpful to practice smiling on demand, so when the time comes for a photo, you will know how to contour your facial muscles into a look you like. To do this, I would start off practicing posing for self-photos (selfsies) with a cell phone or camera, and then graduate to having someone take photos of you if that's an option.
2) The second part of taking good photos is what's going on neck down. Do you have access to photos of people you know on fb? If not, scour the internet and take a look at photos of regular people (not celebrities) in different kinds of outfits (casual, semi-formal, formal, business, business-casual, etc. -- whatever types of situations are relevant to your life) and take a look at how they pose. Who looks good? Who doesn't? What are they doing with their bodies? What is their body language? How are their limbs positioned? What angle is their head at relative to their body? Etc. Ask yourself questions like this, and note the responses. Afterwards, practice these poses yourself. Also, I'm guessing there are webpages dedicated to this question. I'd google it and see what people recommend. Their sites probably include pics, so you might be able to judge the look for yourself and decide yay/nay right there and then!
3) I don't think it's selfish at all. It's understandable many of us haven't had much experience in front of the camera for any number of reasons. Furthermore, losing a lot of weight tends to be accompanied by a change in appearance, perception, and a whole set of learning curves. Taking pictures can be one of them. While sometimes people may think of taking pictures as a 'frivolous' social activity, I think it's just plain smart to know how to present yourself well. It also means that years down the road, you'll be able to enjoy your photos, which seems pretty important... So I wouldn't be shy about asking someone you can trust. If that's still not an option, do you have a camera with a timer option so you can set the timer function to take photos of you? (Set the camera on a ledge, desk, shelf, etc. and position yourself far enough for it to capture your body.) An alternative is to take a video so you can pose and changes poses in real time, and review these later. The latter isn't the same as still-time photographs, but might still be helpful.
Good luck! And congratulations on your awesome achievement!!!
posing for photos - new body issues
