hm....per what I remember from the halfassed instruction I got from my older brother 25 years or more ago... there was some similarity between those two, I remember him showing me the circle bit - but if you look there is a key difference (this is according to what I've been shown, so may need to be taken w grain of salt...that said the techniques worked, screwball aside, seemed that you needed to throw it harder and snap wrist more and differently for the screwball vs curve) the circle changeup, a larger circle, the screwball, small circle, end of thumb on the ball, emphasis on middle finger and de-emphasis on ring & pinky.
just cuz the pic differs from what I was shown for a circle change up