Late replying to this, but even if negative space was a solution to "showing the whole image in the thumbnail", it probably just reintroduces the problem, which

Late replying to this, but even if negative space was a solution to "showing the whole image in the thumbnail", it probably just reintroduces the problem, which is frivolous lawsuits about image attribution not being visible - because of the thumbnail is too small for anyone to be able to see the attribution, they'll sue over that. I'm not sure there's any way around the problem that allowing people to sue over attribution in a thumbnail that clicks-through to the full version is bloody idiotic.