An ArtStation sample can either have lower image dimensions, or have the same dimensions but truncated bit-by-bit quality.
ArtStation formerly had a much more complicated image sampling issue, which can be referred back to by looking at previous revisions of this article or viewing the legacy procedure for avoiding samples at help:artstation. Now a user may errantly upload from image URLs including "/small/" or "/medium/" rather than the correct "/large/" which would be replaceable by a moderator or by uploading the unsampled version and manually deleting the sample. There was formerly a fourth "/original/" which was manually accessible to save bandwidth. ArtStation terminated access to such files reportedly also to save bandwidth.
