The picture posted does not show the vein clearly and an up close examination by a facial plastic surgeon or vein specialist is recommended highly. Most of these can be treated via microphlebectomy with or without sclerotherapy. Better pictures would help guide treatment options.
The picture does not show the vein very well. Forehead veins can be treated by sclerotherapy, excision by micro incisions (2mm) and sometimes laser. The treatment depends on the size and location of the vein. You should see a vein specialist with experience treating veins in this area.