Unsplash.com
A great source for blog post images is Unsplash. The images on here are gorgeous, the website is easy to navigate and the licensing is very clear. All photos published on Unsplash, are free to be used for commercial and non-commercial use. You can even alter the images without needing to give the photographer credit. This is a great site to find an image that you can use in your blog post as the website has a lot of images on different topics.
Search results on Unsplash for the term ‘Beach’
Pixabay.com
Another option is Pixabay, that has both paid and free images. A lot of the images on there do not require crediting the photographer. If you don’t have to credit and you can alter the image, you will find that the image is released under Creative Commons CC0. In addition to photos, you can also find illustrations, vectors, videos and even music on Pixabay.