FOP seems to think PNG Image is an SVG

[David Law via fop-users]

Hi Folks,

I'm reading a PNG Image in our custom ResourceResolver.
It works & finds its way into the resulting PDF.

But...
...org.apache.fop.image.loader.batik.PreloaderSVG reports an error:
/"Error while trying to load stream as an SVG file: Invalid byte 1 of 
1-byte UTF-8 sequence."
/
I've tried this...
return new Resource(MimeConstants.MIME_PNG, uri.toURL().openStream());

...but can't seem to find what type the Resource should have.
(also tried "PNG" & "png")

How can I tell FOP it's a PNG and not an SVG?

Thanks in advance,
DaveLaw