I'd like to keep this thread about how to opt out.

Go to your Contributor page.
Under My Account, select My Profile (
https://us.fotolia.com/Member/Modify).
Select Contributor Parameters (
https://us.fotolia.com/Member/Modify/Contributor).
Find Sell my files on DPC and click Modify.
And, from another contributor: "Then check that where you ticked actually says, "do not share on DPC". It's one of those sneaky buttons that if you press it again it will revert to share." after clicking Modify you need to "Save parameters" at the bottom of the page. Otherwise the changes will not stick.