The URL needs to begin with http://cdn.shopify.com/. If you see

http://static.shopify.com, then replace it with http://cdn.shopify.com.

Shopify’s CDN also automatically creates a copy of your images in the WebP format. If the visitor’s browser supports it then Shopify’s CDN will serve your image as a WebP file. If WebP is not supported, then it will serve the image in the original format (JPEG, PNG etc.)