I don't understand Japanese but I understand a lot about digital images
and their faults. I examined this image and another offered from the
same site by someone in digital.slr a few days ago.

This image (and the other one) has very clear evidence of the problems
which might face 5D owners. Chromatic Aberrations and purple fringing
are the bane of digital photographers. The more tightly packed the
sensor, the more likely to get the faults.

Sigma and Tokina both produce "designed for digital" lenses. The Tokina
effort produces pretty poor quality images when used on a 35mm film
camera but good to excellent when used on a DSLR. I haven't used the
Sigmas. But having the light rays fall at 90 degrees to the sensor can
only benefit DSLR images.

Seeing as the world at large is yet to pass judgment on the 5D, I guess
we'll have to wait and see how good (bad?) the sensor design is at
preventing purple fringing. These early photos are certainly not good news.

Maybe they're tiny pieces of plastic?

Dust motes are tiny pieces of many different substances that flake off by a
fracture failure of the top layers of the (usually) crystalline surface.
There's absolutely no reason to expect any uniformity of size or shape.

That said, there are, as you suggest, many different surfaces inside a
camera from which unwanted images can form ranging from the surface of the
sensor itself to the front, rear, and even internal surfaces of the lens,
diaphragm blades, etc.

   Norm

A couple of questions about this image.
1)Are you sure it was taken with a 5D, the name of the image is
12-24-Kodak-standard.jpg why?
2) the image was taken with a 12-24 f4.5-5.6 lens at 12mm, this is a
Sigma lens not a Canon.
Could this have been taken with a Kodak DCS-N or C? Name of the file
seems to suggest that, would explain a lot of the aberations.
Check Luminos Landscape on the latest user (not quite)review of the 5D.

Tom