Actually, cameras tend to accentuate flaws and a hairpiece often looks better in person than it does in a picture.

That said, I agree with topcat. If you need something that is not detectible to anyone, ever, then a hairpiece isn't for you. I can say with relative confidence that I have never been spotted, but you never know. I'm sure there are times when a fellow hair wearer might have been able to pick out something being "off" but the general public is usually preoccupied with other things to the point where something would have to be pretty far off to raise suspicion.

As far as it being detectable to touch, if you use the right base materials most of it comes down to keeping up with the attachment. As long as all of the edges are glued down tight it would be hard for most people to notice anything different. That is sometimes easier said than done because after a couple of days even the best attachment will tend to lift here and there. Just have to be extra vigilant.