All Things Mopar wrote:

Today Roger N. Clark (change username to rnclark) spoke these
views with conviction for everyone's edification:
I've looked at the images posted in the alt.binaries group,
and find the enlargement job VERY good. It is not
something that can be done in photoshop (CS2), at least not
anything simple. I do see artifacts, but every method has
artifacts.

Roger, enlarging or shrinking do not create artefacts to the
strict definition of the term. These are blobs, streaks,
spots, etc. near sharp corners and often on broad expanses of
color or even brightness/contrast, and are caused almost
excluively by the lossy nature of JPEG compression.

Enlarging and shrinking an image requires interpolation.
ALL interpolation algorithms have artifacts, at least all I've
seen. If you compare your original small image with the
largest one, you can see artifacts. I'll point out one.
From the left, go to the first raised rifle and the guy standing
below the raised rifle (looks like his tongue is sticking out).
No go to the next guy to the right in front. He has a funny smile
with his mouth curved upward in an unnatural way (his left side)
and a line goes almost up to his nose.
If you look at the original image, it is obvious that area is really
a shadow from his cheek. The interpolation mangled the guy's
smile. I suspect the noise that was added in as to mask artifacts,
but in my opinion, was done very well. Other artifacts include halos
around contrast boundaries, a common sharpening artifact.

Roger