Images also work as navigation tools. If a blog has many pages with different images, it will help visitors to remember on which page they are. It will also be useful for people which are looking for specific articles. Choosing relevant pictures for each article is a great option in this case.
If you are making large posts, it's easy for the readers to lose the line which they are reading. Posting images may divide the text into logical parts and reading it will be much easier, without spending a lot of time searching for the required line.