I don't think it's a self-image issue as much as it is a clumsy-compliment issue. In other words, it's not you, it's them.
I remember many years ago when my mom got a haircut and it looked fantastic. To tell her so, I blurted out, "Wow, your head isn't shaped like Darth Vader's helmet any more!" After I said it, I realized that I had perpetrated a dire social gaffe, but she just laughed it off. (In my defense, I was eleven and REALLY into "Star Wars" at the time.)
Your friends and family are just doing the same thing I did--they're so impressed that they just blurt out the first thing that pops to mind, which is to say things like, "Wow, so that's where your waist is!" and other ghastly things.
You have a few possible ways of handling it. One is to continue to stew about it until you make yourself let it go. That can work, if you're actually able to let it go; I'm not, and when I tell myself "let it go" I never do. More power to you if you can. The other is to give someone a gentle reminder that you are still the same you that you were when you lived in your body as it was thirty pounds ago.
You can try it with humor: "Gee, if you're waxing this rhapsodic about my face now, I can only guess what you thought of my 'before' face!" or "Yeah, I decided I got tired of the Buddha-bellied look; I now intend to store all my excess fat in a hump on my back like a camel."
Or you can try it directly: "I appreciate that you notice my weight loss, but it makes me feel as though I must've looked pretty horrible thirty pounds ago and that makes me a bit sad." Take responsibility for how you're feeling and don't shift blame onto them for paying compliments, but let them know how some compliments affect you.
Or you could acknowledge that pretty much everyone has a past self or selves that they now view with rueful amusement or downright horror. I dressed atrociously and had horrible home-cut hair throughout most of high school. I wore ugly-*** clothes and thought I looked good. I used to be fatter. Big deal, the past is past, who cares if we were wrong about ourselves when we looked at ourselves in the mirror back then and thought, "Damn, I look good?"
Because the funny thing is, we DID look good. It's just that now, our definitions of "good" have changed. That's true of your friends and family, too. They thought you looked good before, but now they see that you look even better. It's no insult to be told that you've gone from a 9 to a 10--or for that matter, from an 8 to a 9.
