This issue reminds me of a similar dispute. Let me try to summarize its elements briefly:
1) User:SF (a pseudo username) previously uploaded several old photos of a public figure, claiming to have taken them himself. A comparison of his stated age and the dates of the photos made the claim impossible, but he insisted on it without explaining the discrepancy. However he eventually stopped repeating the claims and allowed the images to be deleted.
2) Another user uploaded embarrassing recent photos of the same public figure that had been widely posted on blogs, etc. That user made a dubious claim of ownership. User:Sf demanded to see proof of the ownership and when none was forthcoming he instigated the deletion of the images.
3) User:SF uploaded a diagram that he claims to have created which also appears on several websites across the world and has for several years. I've asked him for proof of his ownership. He has asked me what kind of proof I require and I replied by asking him what proof he can offer.
Based on the discussion here it sounds like I can hand this issue over to the OTRS/permission system. Aside from the concern that an OTRS volunteer won't know of this user's previous bad faith claims, I'm not sure how anyone can establish the provenance of an Illustrator image or diagram. I'd imagine that ownership of photos could often be established if the purported owner has other, unpublished photos taken in the same place and time. How do we establish ownership of a diagram?
Will Beback