Actually, apparently it is... Or at least that's what pizmogames.com says.
Their "hardest jigsaw puzzle in the world" is all one color - but at least you get to pick your favorite color!
I think what makes it even harder is trying to complete it while dragging the pieces with a mouse or laptop trackpad.
And, actually, just looking at them makes me feel sick. But, since you asked, here are some examples:
But the puzzle that I think tops them all is one that a guy called Dave Evans created to celebrate the Queen's diamond jubilee.
He thought he'd get the party started by cutting a record-breaking 40,000 piece puzzle for a team of jigsaw experts to test themselves against.
However, 7 days before the big unveiling, this happened: