It is just the way it is in China. C'est la vie, eh?

It kinda looks aggressive, but it isn't. It is just curiosity, there is no such thing as a casual glance here; ut it should be taken in the same way.

When I'm travelling and see locals dressed in beautiful ethnic minority clothes, I also feel the temptation to stare a little and take a sneaky photo. I do have a conscience about it, but I recognise that it's how some Chinese must feel when seeing a foreigner. (I used to ask for permission to take a photo of the locals in their finery, but shyness or foreigner-fear led to an almost 100% refusal).

Having said that, I don't find staring a big problem in Kunming and, like posters above, a smile or a wave usually turns an annoyance into a pleasant non-verbal exchange. Leave Kunming for some countryside towns and villages and the staring (and high-pitched "Hello!"s) is much more noticeable. As @tiger said, almost always curiosity rather than aggression.

It's much more amusing in the middle of nowhere Yunnan. Total amazement and curiosity from locals.

even in the Chinese culture, staring is regarded as rude. if the starer really go far to make you feel unconfortable, verbally stop them.

As for people taking pictures of you when you don't want them to, then tell them politely then angrily to stop. That's how the Chinese do it.

Yes, I think if you hold your hand up to block their view, the word 'NO' is universal now. Even some pre-school local kids can be heard using it.

I have been in KM a while and for the most part have adjusted to the stares and pictures, but sometimes it goes a bit too far, though I don't try to show any anger or frustration. A couple weeks back I was just buying doufu on the street and some student type girl started taking point blank photos of me. Her flash was on the first few. I mean she had the camera only a foot or two from me. She would take a few then walk over to her friend and they would look at them and comment on them and snicker and then come back. Finally after a least a dozen I asked her in Chinese if she wanted to take a picture me. Her friend could take the photo. Her eyes widen in shock and she shook her head no while saying "bu yao, bu yao". And that ended the photo session to my surprise. There is really no excuse for that type of thing. It is just rude and primitive behavior and yet best to let it go.

Same thing with students staring at me in restaurants. Looking back over their shoulders at me and my food and discussing something to their friends, sometimes even shifting their seats to get a better look of an actual foreigner eating food. On one occasion it got to be too much and after the girl turned around to look at me and my food the 6th or 7th time I simply said "hi" and waved. She immediately turned around and then never looked back. Retarded really, and you can excuse this sort of thing all you want, but it is annoying but best to let it go and do not do anything weird like stare back assertively. It won't work and can even lead to some sort of strange scene with some Chinese person with mental and emotional problems. Been there too. If it gets weird just speak English to them. "Hi, so do yu want to join me? Do you know any other places to eat? What kind of camera is that?" That tends to scare them away and then you can get on with what you were doing. But I will not let somebody take pictures of me like that doufu stand gal again. I will tell them not to. That incident has sit with me longer than most.

Having lived in several countries for extended periods I learned that the main function of me as foreigner there was to entertain the local population. Ones you accept that position all the stares and sneaky pictures then become a sign of appreciation of your work and being there and life becomes more enjoyable instead of irritating.

One tip.

I learned this the practical way while travelling through Yunnan.

Wear a motorbike helmet with proper visor covering your whole face. Very funny to see the reactions when you take your helmet off. Especially when in rural area nobody wears a helmet and they must have realised that you were an alien.

Works as well with police officers. First let them talk to you for 5 minutes and then take your helmet off to make them understand that you didn't understand a word they were saying. They let you off 100% of the time.

PS: I never tried this without motorbike. Might be even more effective if you actually don't have a motorbike.