Have a friend, in a mask, kidnap one of the crows. Then you appear, and set it free, and give it cookies. (And your friend stops using the mask.)

This makes the assumption that crows can identify people only by the face. It's quite likely they could recognise something else.

That is not so much an assumption as a conclusion, backed up by research:

	▲	Gravityloss an hour ago \| parent [-]
		I think the person meant that it might not be for the mask-wearer. They might be targeted by crows even when the mask comes off because the crows might still recognize them from their walking style or body odor or voice etc.

That's why you use your friend!