Как скрыть alt картинки?

Верстальщику, дайте почитать
ruby.bvision.com/blog/please-stop-embedding-bootst...
и пинок коленкой под дых

You can also apply this same pattern to components and Javascript plugins such as modals which directly depend on DOM elements using Bootstrap's classes. Simply give your elements whatever classes and id's make sense for your application, and then apply the appropriate Twitter classes using jQuery:

$(".my-dialog-class").addClass("modal fade");

не пишем бардак в коде, а добавляем его потом