Should You Ask For Permission When Shooting Street Photography?

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I believe that if you can capture strangers you encounter on the street, whether surreptitiously or brazenly, whether with permission or without permission, as long as the images of the people that you capture are not contrived by any manipulation by you the photographer, and are indicative of humans interacting spontaneously with what ever or who ever is in their surroundings, it’s all street photography.
As far as asking permission, it depends upon the circumstances, if you think you should in any given situation, then do so. If through your body language and presence you can present a non-threatening and friendly, or unobtrusive image of yourself, then click without asking. If it feels appropriate (the subject acknowledged you and seemed responsive) offer a thank you.
Usually I do not ask permission, here is a link to a recent image in which I did not ask permission and nothing was contrived by the subject or myself when I captured the image:

Not a stranger to me...fellow Malaysian.

Just greet them no harm done..then Shoot don't forget to say 'Thank You'

He caught me in action..but later he say 'Thank You ' to me because I bought some spices from the shop keeper.

I ask permission for this shot..that why you see the shop keeper try to rearrange his product nicely.

I always remember this  "Black and white images they enhance emotional substance and have a disposition of making photos look more artistic".