Hilary Duff exemplifies a mild to moderate level of fear in this photograph. She's participating in the "Blessings in a Backpack" food program in South Central Los Angeles. One very classic display of fear is the eyelids are opened wider than normal. I call this characteristic appearance - "white and wide". Ms. Duff's eyes are open moderately wide here. Her eye brows are also elevated - and although not extreme here, this is also consistent with a mild to moderate fear. Her mouth is stretched to the sides with an accompanying display of both her upper and lower teeth. The display of the lower teeth is particularly characteristic with fear.
While certainly not extreme, Hilary's neck muscles' are tightened - again consistent with mild to moderate fear. Another often overlooked and very common signal of fear (although it can be seen with other emotions) is when the head is retracted away from the object/subject of fear. Ms. Duff demonstrates this signal as well.
Although we don't know what Hilary Duff is fearful of, we are certain that for a moment at least, Ms. Duff is in fear of something or someone. It is possible that this photo captured a microexpression of fear. Microexpressions are facial expressions of emotion which are not initiated by the conscious mind and appear for less than 0.5 seconds and as little as 0.04 seconds. The microexpression of fear is very common. Only about 1 in 300 people have the ability/gift of sensing microexpressions naturally, but virtually everyone can be taught to see them. The ability to detect microexpressions is without question an extremely valuable skill in any kind of negotiation, in the court room, in the board room or any kind of high-stakes interaction. How many microexpressions have you missed just today? - hundreds!