I see images offered for sale by some “artists” that larger than you could find on the web, which indicates that they were taken from NASA’s internal servers.
Better get your facts straight before you make an "accusation" of either "artists" or artists. Anyhow, if somebody got supersized images from an internal NASA server and you were, as you claim, responsible for it, then you did a lousy security job.
1. Copyright/use. source here# NASA does not permit use of the insignia and other NASA indicia in advertisements. Any use of the NASA identity on spacesuits and on the Shuttle is generally not permitted unless authorized by Headquarters Public Affairs.
# Any references to NASA in an advertisement must be factually accurate.
# Many NASA images and most film and video footage are in the public domain can be used for advertising purposes. However, there are rules regarding the appearance of astronauts or NASA employees or names in commercial activities.
2. Size. source hereFor instance take image PIA11419.
Size:
4070 x 8024 x 3
Byrd Glacier, Antarctica
Full Resolution: TIFF (97.97 MB) JPEG (7.07 MB)
3. Images from JPL. source hereUnless otherwise noted, images and video on JPL public web sites (public sites ending with a jpl.nasa.gov address) may be used for any purpose without prior permission, subject to the special cases noted below. []
... To use a credit line in connection with images. Unless otherwise noted in the caption information for an image, the credit line should be "Courtesy NASA/JPL-Caltech".