Why do flash pictures look so diff from non flash?

In 'available light' pictures the light comes from everywhere, usually mostly from one side or the other, but also reflected from walls, etc. With the flash, all the light comes from right above the lens, which doesn't look natural. Also the light from the flash is . . . I forget the word. It's designed to be the most effective kind of light so the flash works from the farthest distance with the least power. So it makes your face look all white, and shows up texture. It's a very nasty effect. Plus there's red-eye. Ever seen red-eye in real life? Of course not. People see you as the non-flash, unless the person is carrying a spotlight and shines it in your face. 8^)

I describe the lighting of pictures this way to my students. Natural lighting is like a gentle rain, falling naturally. Some of your subject gets more than some other areas. Some of the rain splashes back to dampen areas that might otherwise be dry. Natural, familiar, and real. Flash lighting is like tossing a bucket of water in someone's face. Very unnatural, unexpected, and often disturbing. In nature, you see light falling on someone from above, or from the side, often filtered by elements that fall between the lighting and your subject. You see things as you do everyday. In flash, you are looking from the same point of view as a floodlight, and seeing the flat, often unflattering reflection. That is why I, and many other photographers prefer natural lighting. And when it's impossible to use natural lighting, we learn to use artificial lighting and flash in creative ways to imitate the natural lighting we all know so well. Serious amateur photographers and professionals learn how to use diffusers, bounce flash, multiple-flashes, and other techniques. With point & shoot cameras, those aren't options. But with SLR & DSLR cameras with detachable flash systems, there lies another whole world. By the way, if your friends see you as a 'flash picture', then you need new friends. I hope that is helpful.

You should have your photo taken by someone who knows how to properly light and pose you. Otherwise, you'll end up with pictures you're not happy with. Most people see you as "non-flash" because we don't have flash lighting going on all the time! Anyway, flash photos can often look unnatural because it's a point source of light very close to the lens. In real life, we have only 1 point source (the sun) and lots of diffuse light, i.e. reflections off clouds, buildings, the sidewalk, etc. Hence, the diffuse lighting is what we expect. Indoors, we have nice diffuse light coming in from windows and reflecting off walls, doors, the ceiling, etc. Again, very flattering light. So, that's the difference--in the real world there's a lot of diffuse light; in taking photos with a flash, that's usually gone, unless someone has gone to a lot of trouble to diffuse the light (i.e. bouncing the light, umbrellas, softboxes, etc.) Don't worry about your appearance--just be the best person you can be and let the inner beauty show.

That's exactly why I take a lot of pictures with a flash (where I'm allowed to) and without a flash. As you said, they're very different.