Addicott Web has a great article which provides a bit of history and explanation into the ALT and TITLE HTML attributes. You might think these two attributes provide the same function but they are used for two different purposes.
The ALT attribute is an important element to the accessibility community. It began as a way for people who are blind and use screen readers (or people who use text-only web browsers) to know when there was an image on the page they were reading.
The TITLE attribute can be used with almost all HTML elements on your website. While the ALT attribute emerged from the accessibility world, the TITLE attribute emerged from the usability standpoint.
From a usability standpoint myself, I enjoy articles which have TITLES applied to images if they don’t already have captions so I can get a description as to what the image entails. As for ALT tags, WordPress makes it very easy to add these and I typically use one to three descriptive words. On the topic of SEO, I have at times received an influx of traffic because of the way I have described an image through the ALT tags.
Have you noticed a decent amount of search traffic coming to your blog by way of Google Image search?