Thanks everyone for the replies.
Syd isn't lame or sore, in fact, he's very energetic in the paddock and while being ridden.
He's never been lame with us, except when he injured his hoof (nothing to do with his legs, could have happened to any other horse) but he recovered very quickly and was only lame for two days.
He is great to ride, walks normally on grass and other horse-friendly surfaces. He walks cautiously when he's on gravel, though.
Oh, and about what loosie said about tying horses solid with a rope halter, those were pics from more than a year ago, when I had just gotten my horse. I didn't tie him there, and the rope halter was too loose, I know :/
He got a new one a few days later, though and I always tie him (with a quick release knot) to the fence.
Proud owner of a Standardbred!