Sounds like a nice topic for someone's MSc thesis!

Interesting question.  However, how it looks to me is the only thing that
matters to me.
Jim

Ever watch "Antiques Roadshow"?
People who know what they are looking at will likely be able to tell from a
close inspection, regardless of size. There are many people in different
professions, not merely antique vendors, who do this kind of thing for a
living.
That doesn't mean they are always correct in their judgments, however.

Anyone worth anything will be able to tell an original painting from an
inkjet, even on the same paper. Prints just look different, the way the
colors merge, may require close inspection but the difference is there.
There are legit artists who sell prints to have lower priced versions
of their oringinals. Most artists I've seen the prints are the same
size or smaller than the originals. The 3000x2000 pixel frame limits
sizes somewhat. I have printed 16x20 from the same size watercolor, I
have done 20x24 prints from 6mp photos with decent results. With a
really good image, very sharp, even tonality you may be able to go
larger. The Museum of Finearts in Boston is selling prints from the
paintings in it's collection. They use a 300mb image from a scanning
back on a 4x5 camera and print on Epson Smooth Fine Art paper lighting
the paining to maximize both tonality and texture, printing on an Epson
9600. The work is incredible but it is definitly a print.

Tom