This is an excerpt from 500px terms:
“The license granted to 500px includes the right to use your Content fully or partially for promotional reasons and to distribute and redistribute your Content to other parties, web-sites, applications, and other entities, provided such Content is attributed to you in accordance with the credits (i.e. username, profile picture, photo title, descriptions, tags, and other accompanying information) if any and as appropriate, all as submitted to 500px by you; ”
“You represent and warrant that:
You are the owner of all rights, including all copy rights in and to all Content you submit to the site;
You have the full and complete right to enter into this agreement and to grant to 500px the rights in the Content herein granted, and that no further permissions are required from, nor payments required to be made to any other person in connection with the use by 500px of the Content as contemplated herein; and
The Content does not defame any person and does not infringe upon the copyright, moral rights, publicity rights, privacy rights or any other right of any person, or violate any law or judicial or governmental order.
You shall not have any right to terminate the permissions granted herein, nor to seek, obtain, or enforce any injunctive or other equitable relief against 500px, all of which such rights are hereby expressly and irrevocably waived by you in favour of 500px.”