To optimize the Images on the website we can use the image resizing option provided by NetSuite. On Website Record there is a option for adding the different size
After adding those size we can use that on the template TPL File as <img src="{{resizeImage url 'main'}}" alt="{{alttxt}}" /> here “main” represents id and we can see ?resizeid=xxx&resizeh=xxx&resizew=xxx along with the omage