Web Design and Development
The alt and title attributes, when used with images, are often the source of many questions because they seem redundant. But even more important, many wonder how the use of these attributes affect visitors and search engines?
Description: Text contained within the alt attribute is used to specify alternative information that should be shown if an image is inaccessible.
So this text is typically shown to visitors if an image is missing, or cannot be downloaded to to a sluggish web server or slow internet connection. It is also shown to people who have disabled images in their browsers. If you have not specified alt text, a missing image is displayed as a blank box or an empty icon depending on browser. Additionally, alt text is typically shown when users hover over an image when using Internet Explorer.
Also, perhaps more important, Google acknowledged that Googlebot uses alt text to determine what an image is about:
As the Googlebot does not see the images directly, we generally concentrate on the information provided in the "alt" attribute.
So for search engine optimization, using the alt attribute is very important.
And finally, according to W3C (the World Wide Web Consortium) the use of alt attributes with images is required for valid HTML.
Description: Text contained within the title attribute is used to display additional information.
The title attribute is primarily important for users. For example, when you hover over an image with title text, the data contained within the title attribute pops up. And with Internet Explorer (IE), which has been known to favor alt text, the title text now takes precedence in IE versions 7+.
But with regard to search engine optimization, it is unclear as to how search engines use title text.