Brendan here from the Shopify Support team.
In short, Image ALT tags are used for accessibility on the web. A person who is browsing your site using a screen reader would need to be able to understand what is being displayed in an image when they're not able to see it. That said, they're also used for optimising search engine result placement by allowing the search engine to accurately index that image to be searched upon.
When you're optimising images it is recommended that you write how you would describe it if you were speaking. Let's use this image as an example:
You should steer way from describing the image as: "cat on couch" or "Cat, couch" and imagine your talking on the phone to somebody while explaining what you're looking at.
"A small cat staring at the camera while perched on the back of an orange couch" more accurately describes this image, and that practice should be applied to all your image ALT tags.
You can read more about this practice and other SEO tools here.
I want to do the text alt description for the images for our products in our shop. My question is for example if i have 3 images for one product, can i put the same alt text for all 3? or should i write different descriptions? Given the fact that is the same product..
Thanks for your help