We've talked a good deal about how to ensure your content is properly indexed by search engines and ranks well for keywords that are important to you.
However, what about when your content is not "readable" as in an image on a page? How do you ensure that the search engine is able to understand what the contents of the image are and in turn drives relevant search traffic to that image and the page that contains it.
The answer to this question is fairly straightforward yet one that is often overlooked: Use the "alternative" or ALT tag to provide attributes to describe the image. Not only is this a good thing to do from an accessibility and usability standpoint but also for SEO.
The syntax is as follows: img src="image.jpg" alt="alternative description here"
As you decide what to include in the alt attribute, make sure that the attribute accurately describes the image and also that the way it is described is such that it optimizes for the keywords that are important to you.
Finally, search engines like Google have image-focused search options (e.g., Google Image Search) which can actually drive quite a good deal of traffic by itself. Make sure to keep that in mind as you create appropriate and relevant alt tags for your images.