In this post I’ll talk about how to ensure you have SEO friendly images on your website or blog. There’s a number of important image properties that should be taken into account: size, name, alts, titles and captions. Let’s start from the top.

Optimize the size of your image

Optimizing the size of your images is not directly related to SEO. However, very large images can slow your page down. And by now we know that Google looks at page load speed as a ranking factor. In other words, slow pages rank worse. The idea is to balance between the image quality (user orientation) and its load speed. In my experience images of 100kb should give you a good balance.

Optimize your file names for SEO friendly images

As in the case with SEO for PDFs as well as regular HTML page names, having a descriptive name for an image file helps Google bot identify image’s relation to content or the subject area. Let’s take a look at a quick example of good image file name and a bad one:

  • Bad example: 12345image.jpg
  • Good example: keyword-topic-image.jpg
This way your file name will contribute to overall page relevancy to your search terms being targeted. For example if your page is about keyword research it makes sense to name images on this page keyword-research-diagram.jpg or whatever is presented on the image.

Optimize your image’s alt attribute

Alt attribute is an HTML property of an image. It’s a textual description for what’s displayed on the image. The purpose of alt attributes is to convey meaning of the image in case it can’t be displayed (images turned off in browser) or the user is visually disabled (in this case browser accessibility features reads the user what’s on the image).

Visual recognition has come a long way in the past few years and visuals can be searches by its forms, using certain software. However, Google and Bing bots prefer to look into image alts to understand what’s displayed on the image. That is why it’s important that your alt attributes contain descriptive content and a target keyword (for the page an image is placed on). Let’s take a look at a quick example of an image that is placed on an SEO training service page.

The above example (in bold) shows the use of alt attribute inside the image HTML tag. You can see that the alt description identities what’s on the image as well as includes the page’s target term – SEO training. Length of the description should be natural, just enough to describe what’s on the image and include a target keyword once. Make sure you’re not keyword-stuffing your image alts. Here’s a great video from Matt Cutts on how to use alt attributes smartly:

A note on optimizing image title attributes

Similar to alt attribute, image title attribute is a property of an image according to HTML cannons. Title and Alt attribute are not the same. Views on the importance of title attribute vary. Based on my experience, title attributes do not bring much value to your images and SEO. Having both alt and title in an image tag is ok, but again, don’t overdo it, make sure it’s descriptive and includes a target keyword.

Optimizing your image captions

If you’re using a CMS or a blog platform such as WordPress or Joomla, you will notice that you can add additional property to your images – image captions. These are things that appear under the image in text and have an ability to hold an anchored link.

Just like with other image attributes, use this option, but use it smartly. Make sure your captions are related to the image, descriptive and include a keyword pertaining to the page being optimized.

I hope this quick overview of how to SEO image files on your website helps make your pages better and more relevant to keywords you pursue. As always, leave your questions and comments in the section below. And feel free to share with colleagues you feel will beenfit by this information.

P.S. If you’re interested in this kind of stuff, feel free to review my on-page SEO factors guide. It’s a collection of articles about on-page SEO elements of your website with looking at real life website examples.