The nub theory is hard to go off though as a lot of people mistake the leg or cord or some other part as the nub. From your image I would say you really can't tell

Like others said from the nub. I had a tech correctly predict my first at 13 weeks using nub theory and with current babe before we got the booty shot our tech showed us this view basically and said it’s a girl, here’s the transvaginal canal then went for the booty shot and sure enough girl.