All artists on Atiblues accept to put their works under various licences, called "free licences". It's not about "royalty free" artwork, it's about work of art which specific rights are free to use. The work stays property of their author, but the author gives few more rights to the user, among them the fondamental one is the right to copy and distribute the work, and the obligation to give credit to the author in all copies or distribution.

So according to the licence the author have choose (there is any of it), when you download a work you will be bound to this licence, that may specify many other rights that can be given (modifying the work and under which constraints, your right to use it for commercial purpose or not) and also the rules that governs these rights. Antiblues let you read the licence before downloading.
Some links to know more about free licence (most are in french, yeah we're french, I'll put some english links soon) :

Arte-radio, repportage sur les licences Creative Commons (flash)
Musique-libre.org, site/portail militant, banque de morceaux copyleft
La philosophie (que nous partageons) des créateurs d'un label en licence libre "another records"

This do not make Antiblues releases "free" works as they do have a cost : time and talent of their author. It seems not incompatible to us to sell work of art and to authorize copying, the main idée is reciprocity, ethic, if we sell something maybe it's because it took its author some cash, or simply because he wish to be paid for what he did. We currently think about a new distribution sheme that will place the artist in the center, supressing all middle-mens, and creat a direct link between auditors and artist. These free licence are a major tool to help promoting artist, and we will use these tools !