Images are fairly important to the success of a blog. Not the only factor though. End of the day, content is king.
People will come back to your blog only if they find something of value.
But images can get people to like the blog or the post page and that can help.
What is the image above got to do with what you are reading?
Well, some could say, it is an image, and others will find it appealing because it is the image of a good looking woman, holding a mac. All about blogging (apparently!)
Here are some best practices to using images:
see this wonderful article | A Complete Guide to Finding and Using Incredible Flickr Images