Images are invisible to search engines, unless they are assigned an Alt code. This is used to add a description of the image that becomes visible when the user cannot see the image or if the image is not loaded properly for some reason.
The purpose of the Alt codes is to improve accessibility of the page as we often host images that are relevant to the content and necessary for users to understand the content. The reason for optimizing Alt codes in SEO is that the visitors who cannot see images are precisely the search engine web crawlers.
Therefore, all images we use on the web should have a descriptive Alt code, containing at least one keyword. These should be placed at the beginning (if not at the beginning, than as closest to the left as possible), because search engines give priority to words that appear first.
A formula that works is the following structure:
Keyword | Description
Alt code with HTML:
Nearly all WYSIWYG editors allow you to edit images easily by adding Alt text, but if one does not allow it, we would have to insert it directly into the HTML code of the page.
To do this, use the following tags:
<img src = “canalip-logo.gif” alt = “SEO | Canal IP”>
Alt Code with WordPress:
To change or add the text in the Alt code of an image that is inserted into a post or page, you must first access to “Posts” and select a post. On the other hand, if you want to modify a page, you must access the “Pages” section.
Once you are in the edit mode of the post or page, click over the image you want to edit, to add the Alt code. Click on the image and two icons will appear in the upper left side of the image. Click the first icon to access options for editing, where you will fill in the Alt code:
Here is a video where Matt Cutts talks about Alt codes: