anyone knows the answer?

It may not be acceptable to put such pictures on the site because it will easily be assumed that the purpose of those pictures is to increase your adsense clicks. you can still use pictures on a real estate site and increase your adsense clicks as well. find very attractive real estate picture and put them inside the content of your site. at that same location, make your adsense ads appear. such a move will not be disputed because the pictures are relevant to your site content the way adsense ads are displayed on sites according to site content.

I believe if you check Google TOS - No "naughty" pictures are allowed on Adsense websites.

I had a blog about six months ago that had pictures unrelated to the posts and Ad sense gave me three days to remove the posts or adsense from the site.

But I think they were more concerned with the relative closeness of the pictures to the ads and not so much the content of the pictures themselves. ( I removed adsense ).

Do make sure the picture you are posting are safe for work and would not be construed as risky or even softcore /NN .. as adsense has been known for simply closing a persons accounts with such content I have known of at least three people. (they deserved it IMO as they pushed the envelope and had junk adult traffic going to their sites.)