Image alt tags appear when an image or non-textual element is preparing or failing to load. The alt or alternative text is required for all images and is a great way to help the search engines crawl your site by providing a textual representation of your graphics. This now allows the search engine robot to index more content form your website.
Image alt tags also offer the opportunity to advertise your site or direct them to another location that may be more viewable. Search engines will get an insight to what your website is about if you include keywords within your image alt tags.
Also, image alt tags are very important is someone were to perform an image search on your keywords. The search results could include an image from your website if you have incorporated your keywords within your image alt tags. Image alt tags are relatively easy to implement and could provide that tiny edge over your competitor’s website.
Click here for an image alt tag tutorial.