The whole debate rose around digital manipulated art...particularly of photographs [chick-walls being a prime example].
Some 'degrees of distinction'...
1. You paint a picture in oils from eye-balling a seascape.
[no problem there, unless you think 'God' my get uptight]
2. You paint a picture in oils from eye-balling a photograph.
[concerns of photographer's composition of subject, but it's a different medium in particular, so less of an intrusion of 'copy']
3. You paint in Photoshop/whatever...digitally from a photograph.
[same issues as with '2'].
4. You paint in Photoshop/whatever...digitally from a 'digital' photograph - scanned in.
[now things are getting 'hazy', as both the source and the product are the identical medium...both bitmaps, say. Now we are in the realm of 'reproductions', more akin than the $20 print of the Picasso you buy at the market.]
5. You cut and paste in Photoshop/whatever parts of the scanned photograph, adding clever [

] lens-flares and such as your personal artistic 'interpretation'.
[now we are specifically at the level of 'plagiarizing' that is endemic in Digital art and skinning, requiring lots of effort to argue and eradicate.]
6. You simply grab that scanned photograph and, using Photoshop/whatever, plonk your name on the bottom and post the 'work'.
[NOW you are a straight, fair-dinkum RIPPER].
Level '5' is where we tend to regard 'borrowed' similarities in skins....[you used MY buttons!!!]....but that is only an issue if the product is uploaded for public dispersal...in other words, the actual 'altered' skin is uploaded.
A screenshot is not an 'actual skin'.
If someone were to DL the screen and reverse-engineer a skin from the shot then THAT subsequent product, if publicly distributed would be in violation of both parties...the ORIGINAL skin artist, AND the poster of the screenshot.
I'll duck over to Devart, catch up with RealitySquared....he's got all the relevant links to Copyrights and their use Net-wise...