Ask HN: What rights does Google have to images it indexes from your site?

I just implemented Re-Captcha on one of our sites. The boss thought Re-Captcha was just a checkbox now, but I explained, if Re-Captcha needs more verification, it'll present images for you to verify.

I showed him this screenshot - https://www.google.com/search?q=google+captcha&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiY2Jat67zRAhUE5CYKHeXDB94Q_AUICSgC&biw=1714&bih=851&dpr=1.12#imgrc=I--dV_Qgm2zQ9M%3A

We rely on SEO heavily for our website and have thousands of photos that Google indexes to help increase our rank.

The boss is questioning where Google gets the images from to use in the Re-Captcha box - I assumed it's from Google Images (which is also where images from our site appear).

Assuming Re-Captcha pulls from Google Images - what legal right to the images does Google have to the images it uses.

Looking for a terms of use or something along those lines. We're more curious then anything really.