Eyebrow hair transplant procedures are performed by doctors who are hair restoration specialists. This requires taking donor hair follicles (from the head or body) and inserting them into the eyebrow regions to create fuller, well defined brow shape.
Many doctors will use very thick hairs from the head. But this can look unnatural in the eyebrow region. Using the uGraft technique I typically use, nape or body hair can be used since it is thinner and a better match for eyebrow hair.
Web reference: http://www.dermhairclinic.com/eyebrow-transplant/