aria-describedby on img tag

This is a long text description of an image used to supplement the alt attribute

NVDA / FF does not read the additional description.

JAWS 15 / IE does not read the additional description.

aria-describedby on img tag in an anchor

This is a long text description of an image used to supplement the alt attribute.

NVDA / FF reads the additional description when the image is tabbed to. It does not read when arrowed to.

JAWS 15 / IE does not read the additional description.

Putting the aria-describedby on the anchor tag instead of the image

Looks like it works everywhere.