Image Alt Tag Definition
Alt is an attribute of the HTML Image tag and is not, contrary to standard usage of the term, a tag itself. The Alt attribute comes from the time when browsers did not support images so that a textual description of the image could be provided. Search Engines are not currently able to read the text that is within an image (e.g. JPEG or Gif) so the Alt attribute allows them to understand what the image is about. This is very handy in image search engines such as Google Images.
Optimizing your Alt for SEO
It is recommended that you clearly and briefly describe the contents of the image in the Alt attribute. For example; if the image is the main image on a page about “building a hummingbird feeder” then you’ll want to utilize these keywords in the Alt. You could make your Alt content something like this: “Building a hummingbird feeder: A step by step guide”. In this example I included the exact keyword phrase that the page is optimized for and even added that it is a “step by step guide” for those who may be searching for keywords like “guide to building a hummingbird feeder” or “step by step guide to hummingbird feeders” or another related term.
Make sure that you don’t duplicate Alt descriptions across different images. It is best to find-tune the Alt description to the specifics of the image and its place in the context of the content. So if you have a secondary image showing how to cut the sides of the hummingbird feeder than you’ll want to describe that in the image. This allows you to avoid duplicate content penalties and to have very contextually targeted images which can be indexed in image search. Image searches can provide quality content to your website.