The content type CMS_IMGDESCR prints alt attribute of a image, which is set through CMS_IMGEDITOR content type.
The usage is very simple. Put CMS_IMGDESCR tag in alt attribute in your module like below.
Note
If you are using more then one CMS_IMGDESCR per article, you have to change/increment index of the next CMS_IMGDESCR .
$descr = "CMS_IMGDESCR[1]"; echo '<img src="path/to/source" alt="'.$descr.'" />';