Bichur * Sorry!, - With your, specific Avatar-I hastened to the statement, but the avatars are used and other people ...
the answers to why have to do with allowing freedom of creation yet protect the rights of the original creator.
 the answers to the Question: Why does one person Web-site "wincustomize.com" allows an image to use and free to download other users, the other person do not, with the image the same, downloaded immediately from the site, (*Ie Web-site to replicate the image already has and uses it)
And question number 2: " Is it necessary, (* according to international standards), confirming the copyright for the image if it is used in the Bootskin XP?
I will explain:
The original image has a size of not less than: 1024х768х24bit= 2.25MB(in format Bmp),
The same image in Bootskin XP already has the size: 640х480х4bit =150KB (in format Bmp)
Ie the secondary image uses less than 5% of the original data, that under international law be permitted without the requirement of copyright
(* In fact, it stretched Avatar, and the avatars do not require confirmation
And third, why in this Web-site does not create your library of images available for beginners? -( not only for Bootskin);
And if some Internet services allow to find the author (Search: like the image) on the original image ...?
Fourthly: "Who could specify: International regulations for the use of screenshots