Alternative Tags (Alt Tag)

Images can create problems for indexing a web page but website without any image will become uninviting and void. Search engines can not read text embedded in images, so Alt Tag or Alternative Tag (HTML tag) tells search engines what the images are all about. It is a must for User agents to render alternate text when they cannot support images, they cannot support a certain image type or when they are configured not to display images. Alt tags are helpful for visually impaired individuals to understand the objective of images. Visually impaired individuals using screen readers or refreshable Braille devices to read the text on the page to them, face a problem when these assistive technologies come across images without alt text, as they are unable to communicate their meaning.
The alt tag is not intended to provide "pop up" text or tool tips when a user's mouse hovers over the image. HTML documents use alt tag to specify text which is to be rendered when the element to which it is applied cannot be rendered. In HTML 4.01, the attribute is required for the img and area element types. To use alternative text correctly and suppress the tool tip that some web browsers generate, a web author can use an empty title attribute.
Alternative text is especially useful in the following situations:
1. People with low bandwidth connections, not opting to load graphics
2. For people using handheld devices
3. For physically and mentally impaired people using assistive technology, such as refreshable braille displays or screen readers
4. Search engine optimization. Many search engines can only interpret the meaning of objects
5. For users with accessibility requirements and users looking for ways to optimize network bandwidth use.

Alt Tag or Alternative Tag optimization Tips:

1. Use alt tag for all images and make sure to incorporate most relevant keyword in your alt tag.
2. Use keywords that are present in title tag, Meta tag and body text.
3. Use 2-3 specific keywords rather than the repetition of keywords.
4. Use plural keywords in alt tag.
5. Alt tag should not be long and must not exceed more than 7 words.
6. Do not make irrelevant alt tag that are distantly connected to images instead use keywords that directly explain the images.
One drawback of alt tag is only Internet explorer supports displaying alt text as a tool tip, which may change. So when a tool tip is needed it is advisable to use the title attribute rather than relying on the alt attribute which was not intended for that use.