Since search engines spiders can not crawl very well an image, there are several SEO techniques used to help spiders understand an image:

  1. use "alt" attribute to describe images;
  2. use descriptive names when saving images;
  3. set the width and height of an image;
  4. use a low number of images on a page or resize them to obtain a smaller image in size

User experience matters for search engines, so having many images on a web page may slowdown a website and the user may wait longer to view the content. Resizing images may increase the website speed.

Images with descriptive names

Using descriptive names, along with the HTML "alt" attribute will help search engines spiders to better understand what the image represents.

From the user perspective, the search engines are focusing on delivering relevant results in their index. Best practices for images names:

  • use names that will describe the images: e.g Joomla-logo.jpg instead of img10.jpg
  • avoid using long filenames
  • save images in a directory used only for images: Joomla! has a special directory for images by default: /joomla/images/
From a SEO perspective, following the recommendations above increases the website chances to be listed in Google Images or in the main index, especially after Google has included in the results page links to videos or images.
Images without the alt attribute

The HTML "Alt" attribute is another on-page ranking factor, having a moderate importance for search engines when evaluating the page relevance. The search engines spiders are not performing very well when it comes to images: they can tell what a image is, but they are not able to describe it accurately.

"Alt" attribute is used:
  • to describe an image when search engines crawlers can't interpret it
  • to improve user experience: there are browsers that can't support images, so users will be able to read the description included in the "alt" attribute
  • the alternative text will be interpreted by search engines as anchor text when the image is used as a link
  • "Alt" text and and file names may increase website visibility in rankings: in the main index as well as in Google Images (or other)

An image source like this one <img src="/image07.jpg"> without the "alt" attribute will not give much information for search engines about what the image represents. Using "alt" attribute <img src="" alt="Joomla! Logo"> will give a better perspective to search engines about the image.

Google Guidelines are recommending to take advantage of this attribute by accurately describing in a few words what the image is. Using 7 to 10 descriptive words will help with on-page SEO and won't affect the website ranking (don't abuse it by stuffing the alternative text with too many keywords because the website risks to be penalized).
Images without the height or width attribute

Best seo practices recommend to set the image width and height attributes, so you can improve the user experience and website speed.

When these attributes are not specified, the browser is forced to download the image and find its size before reading the entire content. Search engines are recommending to specify the width and the height attribute to optimize images.

Seo tips:
  • set the width and height attributes to be W3C compliant; although is a minor on-page SEO factor you will earn extra points in front of your competitors.
  • for thumbnail images use their actual size to optimize them for optimal download times (and reduce bandwidth).

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