HTML image with a null/blank/empty alt

It has been reported that Jaws 7.1 and above ignores an image in HTML if
the image tag has a blank alt attribute like alt=" ". FreedomScientific
claims that this is the industry standard and a WAI recommendation. If
an image has a blank attribute, it is to be ignored by the screen reader
no matter what other attributes it contains. Does anybody know if such a
recommendation exists from WAI? And where can I find that?

Regards,
Stefan