Every image on your website should have alt-text.
Alt text is important for two reasons:
Search engines cannot “read” images. They only know what an image contains if you describe the image using the alt tags.
Not everyone visiting your website can see it! They may be using an app that will read the website to them. Having a strong alt-tag description means the visually impaired can “see” your website better.
Let Plug In SEO write it for you
On your product and collection pages, you don't have to write alt-text by hand. Open Issue Fixes in the Plug In SEO menu, pick one of the Image Alt-Text issues your scan found, and the app writes alt-text built around your keywords and applies it to Shopify when you approve it.
Full walkthrough: Issue Fixes: fix the issues your scan found, without leaving the app
Add it yourself in Shopify
Within Shopify, you can add alt-text to any image directly in the Admin in these boxes:
The text you enter here will appear in your websites HTML code, where it can be used by search engines to determine if your website contains information linked to what an individual is searching for.
You can also edit the alt text from your media library, under Content > Files.