iStock's take on this: http://www.istockphoto.com/help/sell-stock/training-manuals/illustration/quality-standards-custom-fills-and-strokes (includes brushes etc)

just read your ost after my last one.

ok thanks. istock explains the following term: "If you�re submitting files containing effects you didn�t create you may need to obtain a signed property release from the copyright owner (for more information please read the �Property Release� section in this guidebook)."

under 8.4 there is written:

"iStock recommends that a Property Release be obtained when the image contains identifiable property wherever possible. This isn't just for houses, it could apply to pets, cars, artwork and other personal property. The more recognizable and unique the property (and the more the owner's identity might be connected to or determined from the property) the greater the need for a property release.
The Property Release must be signed by the legal and beneficial owner(s) of the property, or their authorized agent. Many of the same formalities apply as for Model Releases.
Note: iStock does not accept digitally created or digitally signed property releases (this includes using script fonts as signatures, e-signatures and scanning signatures and then pasting into the model release)."

that would mean if you use someones'  brushes you have to have a handwritten property release. that's it for istock. i could imagine other agency do it like IS.

i wrote him a message in which i asked him if i would be allowed to use his free brushes to make illustrations out of them, that i want to sell in the internet. he said "Yes, you may use them in your commercial illustrations."
in context to my question that would be my property release i think. but it's useless aslong i have to link him back. right? i understand if i want to sell free ones i have to ask him if i have to link him back and if i'm allowed to sell images containing his resources.
in the terms of use is also written:
"You can use our resorces in your projects and you are free to sell, distribuite and release your products; but you can�t resell or redistribuite the original files. In example you can use our icons in a web template and sell it, distribute the icons you�ve used along with the theme, but you can�t re-distribute the entire icon pack; or you can use our vectors to create a t-shirt graphic and sell the t-shirt, but you can�t re-distribute the entire vector set."
that would mean i just have to modify the resources i have to pay for and then i'm allowed to sell them as stockfotos and don' have to link them back but i can not sell the free ones because they are under a creative commons 3.0 unported license and i have to link them back like i've already mentioned below.
sorry but i have to know that as acurate as possible.

in the second case it is a mix of both vector and brushes: "Free Floral Vector & Brush Pack...File format: Eps, Ai, Abr brush & Png"
I thought it would be allowed to make an unique illustration out of these brushes and that it would make a difference to just reselling the content of the pack. you know what i mean?
i was just wondering at all the floralillustrations and similar pictures on stockfotosites. should all of them are made out of self-made brushes by the appropriate author of the illustration?
another example would be all the illustrations that contain photomaterial of the earth. some of them are e.g. foto material you can download from the site "visibleearth.nasa.gov". the nasa allows to use their fotomaterial to sell pictures made out of them but requires a link. i've already asked them personally.
however i heard of some stockfotosites that doesn't accept nasamaterial anymore.
so back to the brushes. is it common that illustrators on stockfotosites use their self created brushes or some downloaded stuff?

johoe!