Users (and Google) like websites that load quickly. So its important to speed-up your blog or website. One really easy way is to optimize images on your site. Lesser the size of images, faster the site. Its as simple as that.
Here's a free online tool that optimizes images. Its called Web Resizer.
Head over and upload an image. Additionally, you can change the width/height, contrast etc of a photo. Just do enough to reduce the filesize of the image. That's all.