Does the emergence of a small amount of blood (like a drop) as a result of intentionally picking one's skin during fasting necessitate making up the fast?

Blood coming out of a fasting person does not invalidate their fast and does not necessitate making up for it. Even according to the Hanbalis, who consider cupping (hijamah) to break the fast, a wound, venesection (fṣd), or nosebleed (ru'aaf) does not break the fast.