In the education field, it is known as differentiated learning. When you approach a subject, a lesson, a lecture, anything that is imparting knowledge, from multiple angles of attack, thusly getting more exposure and activating more of the brain in the process. The theory really is quite simple. The more parts of the brain that you engage with the same subject matter, the more likely the learner will stay interested, and the more knowledge they will retain.
The same thought process can be applied to your blog. It does not matter how excited you are about the subject at hand, if there is not something there to immediately pull the reader into the blog, they will not stay to read the whole thing, but they may not even stay to read your opening paragraph. It is even trickier with blogs than with students, because people on the internet can be off to visit 30 different sites in seconds with just a few clicks. You have to convince your readers that your blog is worth reading within the first three seconds that they even set eyes upon your site. This can be done with catchy headlines, sure, but images are just as, if not more, effective.
That is why you need to search for free blog images. You can find plenty of sites out there with free images for blogs and free infographics for blogs, so the real trick is slogging through all of the generic pictures to find something really relevant. I cannot tell you the number of business blogs that I have seen with Generic Businessman Giving Thumbs Up To Camera plastered on its front page. Or Office Worker One and Office Worker Two Standing Around the Water Cooler. No one laughs like that at work.
If the picture is just generic, and does not actually pertain to the article, or is not interesting enough, no one is going to read your article. When you get some good free images for blogs on there, not only will it engage your readers, but it will help to illustrate the point of your blog, making sure that your readers really take away what you are trying to say. So stop posting essays with nothing to illustrate your point. Posting pictures can improve reader retention and even encourage return traffic.