All images should have an alt tag – even if it's a null tag. Use a null alt tag (alt="") when labeling spacer images or design elements that don't need to be read. This will allow screen readers to skip over/ignore those elements. (Note: using a null tag is not the same thing as using no tag at all.) Your alt tag should be more descriptive of the image content than the image's file name. For example: (img src="dog.jpg" alt="beagle puppy chewing sock"). If your image performs a function, you also need to describe what it does ("search our site" or "submit form"). When an image contains only text, the text being displayed can usually be used as the alt tag. An example of this would be a navigation button, such as Products. The content would be identified in a screen reader as a link, so there is no need to say "Link to Products." If you are showing an image of a specific product, publication, or person, use the full name. (Green and white Apple Watch band, Cover of 2016 Buyer's Guide, Joe Smith, CEO.) Try to limit alt tags to no more than 5 or 6 words. Don't be redundant. Don't repeat the surrounding contextual copy for your alt tag, or stuff alt tags with keywords. Don't use the phrases "image of" or "graphic of" to describe your image. It is apparent to the user that what is being described is an image.