Help - Haow is it with images?

You can't have copyrighted content such as text or articles, but how's it with images?

Can I use images at my blog? I I'm doing review affiliate, do I need Public Domain images, since it is for commercial use?
What about normal post without affiliate link in them?


+ One little bit off:
Can I post any image I like even with copyright to social media as FB, twitter, ...

Thanks! Cant find answer anywhere..

As far as I know one of my friends in UK went to court because he used copyright images from Google. Use sites like Tumblr for images.