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Screen reader interpretations of images in text (not part of a link)

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From: Birkir R. Gunnarsson
Date: May 7, 2012 9:43AM

Oh yea wise ones.

I was asked whether having a widespace inside the alt tag for an image
would cause screen readers to read it.
For this I cooked up a minor test. The answer to this is that Jaws
didn't but NVDA does with FF10 at least.
But along the way I discovred something else that really surprised me
Neither Jaws nor NVDA (tested with FF10 and IE9) indicates the
presence of an image in a webpage when it is missing an alt tag (see
example one in the attached document).
Inother words.
If you insert an img tag with a src attribute, it is treated by both
Jaws and NVDA as if it had an empty alt attribute.
For some reason I always thought that screen readers should indicate
the presence of the graphic and read the path or filename of the image
file.
I know they do that when the img is inside of an anchor tag, but was
surprised to see that they do not when the image is inserted by
itself.
Is this something everybody knows and I just discoverred?
Is this best practice for images (seems to me that users may want to
know about images in text even if people have forgotten to indicate
that they are decorative by setting the alt tag to ""), or is there a
coding error in this document somehow (hand coding HTML is something I
need to practice honestly, but I see no problem with the file, other
than I did not specify a layout for the imges).
Cheers
-B