Sorry to butt in Peter but alt text is not a featured article requirement See WikipediaFeatured article criteria number  Media Alt text was a FA reqirement briefly about three years ago and this caused so many difficulties disagreements and squabbles that it was withdrawn as a criterion and became voluntary You have discretion here but for the sake of consisrency it should be all or nothing if editors choose to use alt text then it has to be used in all that articles images not just some