Images of any kind, be that illustrations, graphics or photographs, are effective additions to your content. To follow good practices for both accessibility and SEO – each image has to include the alt/alternative text.
This is a short description of the image content — this will be shown on the page should the image fail to load, be read out by screenreaders and other assistive software as well as being accessed by search engines.
You can check on your images’ text settings by going to the media library and clicking on the image. This will bring up the details of the file and you can update the text alternative at any time.