For SEO (Search Engine Optimization) purposes, it’s best that all elements of your web site are optimized. A lot of times, people focus on text content, forgetting that images can be optimized, also.
What criteria should one take into account when optimizing images? I list below the most important criteria:
- Most important criteria: ALT text. This is a tag which is mostly invisible for the end-user. You can view the ALT text for a very short time, before the images on a web site finish loading. Also, some software used by people with visual impairments reads this text out load. But for the search engines, the tag explains very easily what the image is about. It’s by far the most important element when optimizing images.
- Second most important criteria: image filename. Less important than the ALT text, the filename also explains what the file is about. The words separator should be the hyphen (“-“).
- Text surrounding the image. Images are generally in a larger page, which contains some text, like in a blog post, a descriptive page with text, or an e-commerce product. For all of these situations, the text surrounding the image helps explaining what the image is about.
- Image compression. Helpful for loading the page quicker, and useful even more when seeing a page on mobile. It’s best to use JPEG file format with a compression between 75-85%.
- og:image tag. This helps the page look good when shared on social networks. Find out more details about the tag here.
Note: Also see the Yahoo! Group on which I present similar issues: IMRo. To join, email email@example.com and reply to the confirmation email.