Don’t even think of using the ALT attribute (often called the alt-tag) any other way than outlined in the W3C Accessibility Guidelines – 7.1 Short text equivalents for images.
The alt-tag is there for the many users who use talking browsers, screen readers, text browsers or browsers on small devices. If you are blind the last thing you want to hear from your talking browser is the text in an alt tag stuffed with keywords.
Use short and clear alternative text for every image that carries information and use alt=”” (nothing between the quotes) for non-link images that do not convey information or are redundant.
Remember search engine spiders are ‘blind’ too and if you write perfect alt text for a blind user it will be perfect for SEO as well.
alt=”store fixtures and retail store fixtures with fixtures in the store” (Let Google know you are an alt tag spammer)
alt=”Chris Day” (Bad)
alt=”Chris Day at work” (Better)
alt=”Google engineer Chris Day seated at his workstation.” (Perfect!)