This is an absolute basic SEO tactic, but everyone forgets it consistently. Alt tags for images not only help explain to Googlebot what images are on your site, but can be strong SEO juice in and of themselves. Google will be able to understand what each image is and how to index it. Keep your alt tags relevant to the content on the site and the image itself so that it both explains what’s going on in the image and what the content is that surrounds it.