Board Thread:Support Requests - Getting Technical/@comment-34032382-20171220213133/@comment-32354545-20171221063218

Dunnoob wrote: TinEye saw this image in 2013 on http://illustrateyourworld.tumblr.com

IANAL and have no idea how to find a license or copyrights on tumblr, and of course this might be also stolen copied.

That site gives https://ivanlaliashvili.deviantart.com/art/Portals-7th-heaven-399845666 as a source. It does not rule out the possibility of plagiarism, but DeviantArt is a very plausible place for the material to have been posted by the original author. You may contact them there for permission.