I will respond in support of @eidolem & @tippingpints request here.
Every image should have its own alt tag. This is a core concept of Google’s SEO standards.
Alt text (text that describes an image) improves accessibility for people who can’t see images on web pages, including users who use screen readers or have low-bandwidth connections.
Google uses alt text along with computer vision algorithms and the contents of the page to understand the subject matter of the image. Also, alt text in images is useful as anchor text if you decide to use an image as a link.
Image SEO Best Practices | Google Search Central | Documentation | Google for Developers
Further, Google’s John Muller has explicitly stated the importance of including alt tags for images for some time now:
Beyond the confirmed SEO importance, it also is an accessibility issue for those with visual impairment who rely upon alt tags for navigating the web via screen readers or other tools.