Visuals are a very important and useful part of a website and blog posts. They can capture the readers attention and break up the words on the page to make more readable.
The use of images is governed by copyright laws. One way to avoid any problems would be to only use original content – that is, photos taken by you or by a photographer you hired.
When that’s not possible, make sure of stock photography websites. You do not own the photos on those websites, but they grant you a license (i.e. permission) to use that image. You can use creative commons for images. This requires attribution and certain terms but is a good way to stay compliant.
Assume you need permission. Any time you are using someone else’s photo whether you found it on their website, google image search, or otherwise, you should get permission for the use of it.
If there’s a particular photo that you want your audience to see but are unable to get permission, then you can link to the url of where the photo is. This way you are not infringing but your audience can still see it. I know that’s not ideal but you should be careful embedding a photo without permission and this is a good work around.
Short answer is that if you don’t own it, then get permission!