Draw a line from your knee to your elbow...that line should be perfectly straight (or as close to it as you can get). Really, you want your whole shooting arm to be perfectly straight with your shooting (plant) leg. Blair's arm is not straight and is too inverted close to his head. Some guys like Reggie Miller can get away with that. A guy like Blair needs to straighten his arm and move it farther to the right to get more symmetrical, balanced jump/3 pt shot. Basically, his release/hand is way too close to being parallel to his head...that's not a good form.
That's just how it looks it that pic though. In real time, it isn't as bad.