If there is a single concept that is the driver of much of the Internet's growth over the past decade – not to mention nearly all of Google's annual revenue of $25 billion – it is the concept of keywords. Keywords are what we type in when we are searching for products, services, and answers on the search engines, an act that Americans performed 15.5 billion times in April 2010 according to ComScore, the web research firm.
QUOTE: “alt attribute should be used to describe the image. So if you have an image of a big blue pineapple chair you should use the alt tag that best describes it, which is alt=”big blue pineapple chair.” title attribute should be used when the image is a hyperlink to a specific page. The title attribute should contain information about what will happen when you click on the image. For example, if the image will get larger, it should read something like, title=”View a larger version of the big blue pineapple chair image.” John Mueller, Google
Your SEO keywords are the keywords and phrases in your web content that make it possible for people to find your site via search engines. A website that is well optimized for search engines "speaks the same language" as its potential visitor base with keywords for SEO that help connect searchers to your site. Keywords are one of the main elements of SEO.