What can I add an ALT tag to?
Alt-text, or alternative text, commonly referred to as alt tags can only belong to an image. You can't add an ALT tag to a page. For example, an image of a dog on your homepage can have ALT text, but the homepage itself doesn't. The homepage contains many images, with each image having its own ALT text field. .
All images should have alt text, regardless of where you place them on your shop. Not only does it provide search engines with information about the image but this could also help you and your shop to show up for a particular search query.
Alt text not only help search engines “see” what images are on your site (search engine crawlers cannot see pictures, only read code, including alt-text) they are also important for accessibility for users who may be vision impaired and have the website read out loud to them.
Alternative text needs to describe an image so someone (or a search engine crawler) can see it in their mind! You wouldn't describe a image of a Dalmatian as just "dog". You'd say "a medium sized white dog with black spots".
The only images that should not include alt-text are those that are purely decorative, such as graphic design elements like swooshes or arrows.
To add alt text to your images in Shopify, follow these directions: Alternative Text for Images
Or, with Plug in SEO Plus, you are able to add code to automatically generate alt-text based on the product page the image appears on - a huge time saver for many online shop owners.