Pixabay.com provides free public domain images that you can use in your blog without the requirement to acknowledge the source.
You are free to use Pixabay images for commercial use, without seeking permission. There is no cost for these high quality images.
The range of public domain images is not as extensive as you will find in some of the paid image sites, but the quality is superb as in the image below:
Some of the top categories of Pixabay images are as follows:
You can just sign up to Pixabay and get free access to a wonderful range of images that you can use on your blog or website.
These public domain images will enliven your blog or website and enable you to illustrate aspects of your posts or articles.