From SEO perspective, Do we need to have a unique image as 'Featured Image' (Shopify) or can use any image from product pages?
The featured image must be unique but relevant so you can use the product image with different sizes (recommended size for the featured image so it can fit the canvas and will be visible). A unique featured image means here is to show an appealing image that will help the customers easily understand what the product is about. The main factors here to consider are Relevant alt attribute to the image Relevancy to the product Title and description of the product
You need a unique image or you will be copying someone else. You dont want google to see you as a copycat