If I purchase a merchant resource kit that specifies it is copyright free so long as the resource is altered -
What is the legality of that merchant asking/requiring me to leave the original copyright notice on the texture maps?

I understand that it may be the polite thing to do , but I want to know if there are any grounds for REQUIRING it.
Thank you

Vendor resources are being sold as an extension outside of the normal Renderosity license (which usually states that you can't redistribute any part of the product in any way.)

Therefore, vendors are free to put certain usage restrictions on their resources. Common restrictions are:
Listing the item as a credited resource or leaving copyright marks intact
Must change X% of the resource
Must not use more than X parts of the resource
Must only be used in commercial packs, not freebies
etc.

Yes, the original artist can restrict the license in whatever terms they desire.

Please also keep in mind that you can't make a resource pack from resource packs.

Anymore I ALWAYS completely read the readme before purchasing ANY products from Rendo.

I read the entire read me on this one as well before adding it to my cart.  I was agreeable to all of the restrictions and so proceeded with purchase.
Upon reviewing the resource after purchase I find another notice pasted directly on the texture images.  I feel this is unfair practice.  The preview resolution of this notice is too small to read.

I feel that merchants should be required to place ANY and ALL restrictions within the readme and NOT in places like on the texture that can't be viewed before purchase.  Failure to do this results in yet again having to spend time asking for a refund.

Hi JJ,

Could you please drop us a line at store@renderosity.com so we can take a look at that. We would normally expect any restrictions to be in the readme.

Will do Karen, thank you for the response.

Welll I guess I have to correct myself
I looked at the product page again and there is a notice:

""Another important note to avoid further misunderstandings:
There is a note on all texture maps with my copyright on it. It would be very nice if you could leave it there (when selling your final product), but you don't have too! It's up to you - but as I wrote: It's a nice gesture if you leave it, but if you don't want to, that's fine and you are free to remove the copyright tag (but include it in your read-me at least)! ""

Apparently I didn't read enough - not sure how I managed to miss that, my apologies!!