I think that you have to answer the question in the title in the context of the circumstances. I’m thinking of tigers in the wild and in captivity. However, the underlying factor which dictates how tigers react to humans is their character. In regards to the human-tiger relationship, tigers prefer to avoid people and generally give them a wide berth, in the words of Fiona Sunquist, writing in Wild Cats of the World.
In the wild
The famous tiger hunter turned conservationist, Jim Corbett, after whom a reserve in India is named, describes the tiger’s character very well and he should know. In his book, Man-eaters of India, published by the Oxford University Press in 1957, he writes: “Tigers, except when wounded or when man-eaters, are on the whole very good-tempered. Occasionally a tiger will object to too close an approach to its cubs that it is guarding. The objection invariably takes the form of growling, and if this does not prove effective it is followed by short rushes accompanied by terrifying roars. If these warnings are disregarded, the blame for any injury inflicted rests with the intruder.”
I take from this, that tigers in the wild general disregard people. We see tourists in vehicles in India’s tiger reserves looking out for tigers. One of them crosses their path perhaps no more than 30 feet away. The tiger ignores them. I’ve seen a photograph of a tiger no more than 40 feet from a couple of men on a motorcycle on a road in a reserve. Once again the tiger ignored them. I think this is the default reaction by a tiger to the presence of humans. They are not particularly interested as long as humans stay out of the way.
This is because the human is not a prey animal for the tiger. They rarely attack people in the wild and it seems fairly conclusive that if they do so it is because they have to due to injury, infirmity or old age. It’s about survival and they pick on a human and become a man-eater because they are easy prey but it is unnatural for a tiger to do this. They can be deterred because they attack from behind and if the person wears a mask depicting the face of a human on the back of their head it protects them from a tiger attack. Farmers also paint faces on the backsides of cattle for the same reason.
I think it’s different in captivity. We hear of tigers attacking zoo employees. We also hear of private zookeepers being attacked by their ‘pet’ tigers. There are strict protocols to protect zookeepers when working in tiger enclosures. Sometimes these protocols are broken with fatal consequences. My argument would be that tigers in captivity have no means to express their natural hunting desires so as soon as the opportunity very rarely presents itself the tiger leaps into action and instinctively attacks and sometimes kills. But in the wild they have the usual prey animals to attack, kill and eat. They are unconcerned about humans.
So how do tigers react to humans? Instinctively they tend to ignore them and are, generally, good-tempered. It’s just that under certain circumstances their instincts take over and they become ferociously lethal to any human in their vicinity.