Use of non-copyright images in blog posts

When I write an article, how do I choose the right images so that I won't fall into copyright problems?

I checked into a few sites like flickr, gettyimages, unsplah. But in gettyimages we have to pay to get the photos we need. And unsplash is just hopeless if you want to get the correct photos. If I search for someone's photo I will probably get a completely unrelated photo. Another idea that I had was that I would just save an image from Google and then in the caption I would write the source of the picture. But still, I am worried that it might get me into some trouble.

So, if you guys don't mind, could you guys let me know how you guys get the images/photographs of people you need?

Edit: Thank you guys for all the replies. They were really helpful. I will correct my mistakes.