Someone wearing glasses is always a problem for photographers. Shooting a 'straight on' portrait, with a camera mounted flash is a sure-fire way to get flash-glare in the lenses of the glasses. Although I've never been a portrait photographer, in watching a couple of them in action (shopping mall, etc) they always have the people/kids look a little to the left or right of the camera, thereby eliminating the reflection of the flash in the glasses. Outside, the same is true, but the sun is coming from various angles and reflects at similar angles. Think of a pool ball bouncing off a cushion...the angle of reflection = the angle of incidence. The same applies to light reflections.