How to make image alternative text as required be more web accessibility?
I found one of the solution by using EIM module. I understand this is not the best solution but this module able to enable Alt field required on image field by content type.

---- updated info on Aug. 22nd 2014 @ 11:12pm
The EIM module adds checkboxes for the fields of image editing forms by content type. Including "Alt field required" and "Title field required". See below screenshot for details.