Depends on the artifact and ...
uh...
What caused it

Ok like digital photo's can have digital artifacts caused by an error in the operation of the camera.
Or, When you transfer the picture from the camera onto your computer and then send it out, compress it, decompress it, these can cause artifacts as well.

Light can cause reflections, glares, flares, etc.
See CD here.
Warning!: Some naughty language.

Next, an old photograph (analog) can have artifacts from the chemical process of developing them, age, or exposure to light or other chemicals.


This particular one looks like a reflection on the glass in front of the astronaut to me. If you zoom in, it looks translucent. You can see the background through it.

__________________
"Hope is not the conviction that something will turn out well but the certainty that something makes sense, regardless of how it turns out." -- Vaclav Havel

Quote:

We just don't know much.

Yet if not for those words, what would science be for? - KaiYeves

I propose an ATM corollary to Godwin's law: an ATM'er will inevitably compare himself to Copernicus (Or Galileo), when the going gets tough. - CodeSlinger