It's not usually a good idea to put the same alt text on every single image. It kind of defeats the purpose of its use.
Alt text is intended to be used as an accessibility feature and also display in place of an image when the source URL is broken or if a visitor turns off images by default. Search engines also use this attribute to help determine what the image is when crawling your site.
You're actually doing your website a disservice by making every alt attribute exactly the same.