Using images in your posts is important for your visitor. Nothing is more irritating than a site with only text. There are millions of images on the net that you can use for free without giving benefits to the source. The feeling if you visit a website with good images in the posts is just 10 times better than a site with only text. You need to create a nice feeling on the site so people will stay and not bounce away immediately.
People read 40% of the speed that they read in a book or magazine. Reading on a screen is harder for your brain and slows down the speed of reading big time. It is nice for the eyes and brain to see an image once in a while on a site. That is why I use at least 1 image in every post I put up. Also make sure your posts are not too long.
A few sites I get my images from:
Makes reading a pleasure