The higher the size and quality of an image, the longer it takes to load. If you have amazing graphics and an image or two (or more) with every blog post, your loading time will be slower.
There are a few ways to address the image issue. One is with Lazy Load—a process that loads only the images appearing “above the fold,” or on the part of the site a visitor is actually viewing. You can do this automatically with the jQuery Image Lazy Load plugin.
Another image optimizer program like Yahoo!’s Smush.it. You can use the tool right from the site to compact images (without losing quality)—or you can install the WP Smush.It plugin to have it done automatically when you add images to your site.