Please look through the earlier Q&A: there's a similar question to yours. But I'll add to what I've said. To answer you question, and at risk of sounding sententious, I approach photographing people like all of my relations with people (or try to): with honesty, openness, directness. I guarantee not one was taken 'subtly' as you call it: every shot was in full knowledge of the subject - sometimes with explicit permission, sometimes with indifference. By 'subtly' I think you mean 'sneakily'? I wouldn't post anything I shot sneakily, unless e.g. I was in a group of hostages. And yes, in some countries it's illegal simply to take a sneaky shot, let alone post it online. So watch it. You sleep more easily when you're open and honest about everything, including your photography.