This took about 10 minutes to 'extract' and clean up to re-use as a 1024x768 bitmap of reasonable quality......would have been faster except I forgot there was a cursor to be removed....
Because it is quite simple to 'get' the wall from an unobscured screenshot, and IF the wall is not your own photo/art then it is arguable that even 'fair use' does not cover the image's inadvertent re-distribution by way of a desktop screenshot.
Don't be fooled by arguments about image 'quality'.....this 'altered' screenshot is third generation jpeg.....the extracted 'wall' is quite acceptable resolution/quality.
Any screenshots where it is deemed a simple matter to extract the wall image will be rejected, unless it is stipulated with the upload that it is the artist's own work.
Crediting an author will not absolve you or free you from this issue as the original artist has no direct control over your screenshot upload, ergo it violates his inherent copyright....