How to properly credit an image or photo from a brand I'm writing about.

I write articles about brands and companies on my website. For example, hotels, fashion, technology, etc. When I do this I usually take images from their Twitter and Facebook accounts and sometimes website for the post. My blog is relatively new and I plan on monetizing it, so I do not want to get into trouble with copyright later and want to make sure I’m crediting their logos, photos and images properly. Please advise;)