Thanks for this test case Hitman, I was struggling why my image submit button that didn't work. And the required value attribute is quite weird. It doesn't need to have "submit" anything should do, but I'm still not getting why value attribute is required on this type of input field.
Just a note to all who have been posting before: the alt attribute is not supported on <input> element at this time. It doesn't validate.
Kind Regards,
Márcio