I recommend Facebox or UIfaces for those times you need real-looking people in your mockups.

So am I now restricted not to use any woman in bikini? Or a woman wearing tan top? Are you saying by choosing a female in tan top is bad?

I don't see why we can't use those photos. I don't think people are sexualizing women. Sexualizing sounds like we are making a woman sexy. I am on Tumblr daily and I see a bunch of bloggers using sexy photos to attract followers so maybe we should stop doing that. I see instagram full of sexy photos and I guess we should stop doing that as well.

The iOS example seems off and I would agree with OP that that photo is questionable. the other two are fine. The second one doesn't really sexualize women. Just because the designer found a bunch of women avatars doesn't mean they are sexualizing women; maybe they haven't found a good looking guy avatar. Maybe those are friends of the designer.

The third app is also fine. To be fair, make a poll and ask how many women like seeing a beautiful woman picture than a man's picture.