Image optimization for internet search

Published: Nov 13, 2021

Images make your content more attractive and engaging but using them is also important for SEO and web accessibility. Google Images is a search service that allows users to search the internet for images. It was launched in 2001. An important part of image optimization is properly filling out image alt text, which can help you to rank better on this service.

Optimising images for search

Outline of the article:

  • What is it so-called alternative text
  • How to write alternative texts
  • Their importance in terms of SEO
  • Tips for correct use of images on websites
  • How to evaluate success of image optimization
  • Most common image formats for websites

What is so-called alt/alternative text?

Alt text (attribute alt, sometimes incorrectly used “alt tag”) describes the content of an image for visually impaired people and robots.

  1. Adding alternative text to images is primarily required by the site's accessibility policy. Each non-textual element carrying a meaningful message must have a textual alternative.
  2. If the image does not load, the text filled in the alt attribute is displayed.
  3. Alt text provides better context/description of the image for search engines, which helps them to index the image correctly.
  4. If you link through an image and have alt text filled in, the search engine takes it as anchor text (descriptive text of the hyperlink).

In the context of images, you will also see the image caption (Title text). What is the difference between them? The alternative text is shown to the user when the image cannot be loaded, while the caption text is shown when you hover over the image.

The Search Engine Optimization Starter Guide (Google Search Central) states the following about using alt text: "Optimizing image file names and alt text makes it easier for image search projects like Google Images to better understand your images. (...) Don't populate alt attributes with keywords, as this will lead to a negative user experience and cause your site to be considered spammy."

How to write alternative texts

Alt text should not exceed 125 characters. Screen reading tools stop reading this text further in case of a longer text.

Write descriptive, concise and relevant alternative texts.

Do not start an alternative text with “This is an image of...” but go directly to its description. Do not insert key words to the alternative text of every image. If your blog post contains a few images, it is enough to mention the key word in one of them. Choose the image, which you think best describes your topic.

Can alt tags affect positions in Google image search?

In August 2021, during a Twitter discussion about the SEO benefits of alternative text, Google developer Martin Splitt said:

"Yes, alt text is also important for SEO!"

Tips for correct use of images on websites

  • Provide good context: Make sure your visual content relates to the theme of the page. Only display images where they will enrich the content on the page.
  • Choose the best location for the image: If possible, place the image near relevant text, or consider placing the most important image near the top of the page.
  • Do not insert important text into images: To ensure maximum accessibility of content, keep text in HTML and include alternative text for images.
  • Create informative and valuable pages: quality content on your site is just as important to Google Images as visual content - it provides context and makes the result more usable. Page content can be used to generate a text snippet for an image. Google considers the quality of the page content for image placement.
  • Consider the user-friendliness of sites for different devices: users search Google Images more from mobile devices than from computers. For this reason, it's important to design your site for all types and sizes of devices. Use a mobile usability test to see how your site performs on mobile devices and get feedback on what needs to be fixed.
  • Create the right URL structure for your images: Google uses both the URL and the file name to understand your images.

Source: Google Search Central, „Google Images SEO Best Practices„.

How to evaluate the success of image optimization?

For example, you may use Google Search Console tool for that. Click on the Output in the menu on the left and then switch the Search type for Image

In the Google Search Console, you can further find the following metrics:

Total number of clicks

Total number of views

What are the most common image formats for websites?

  • PNG (Portable Network Graphics) is meant for images with lossless compression. Photos are not suitable for the PNG format due to the absence of lossless compression.
  • JPEG (Joint Photographic Experts Group) is suitable for saving photos or similar content.
  • WebP was commissioned from Google in 2010. It supports lossless coding. It is conceived as the JPEG and PNG substitute.
  • AVIF was introduced by Alliance for Open Media in 2018 as a part of open format AV1 video coding. This format has generally better compression than WebP, JPEG, PNG and GIF and is designed to replace them.


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