Thanks for your replies guys, it was basically what I figured. As said, it's hypothetical, I'm not intending to sell the pattern anyway. I just wonder where the lines start and finish - like someone knitting stars into a wristband, I'm sure somewhere there's a pattern to be bought for that, but does that preclude that person making up their own pattern for stars in a wristband and selling them?
It's a different case, because in the ds case one I actually *was* inspired by someone else's work, but what happens when someone just comes up with something that someone else has already done like that? Say I'd not seen the scarf pattern, but decided to make a binary ds case in black and green since they're standard computer geek colours, would that still be violating copyright? And how, in the world of the internet, could anyone prove they had or had not seen a pattern or a picture somewhere in their web travels?