I have a dent on the right side of my forehead with a vein in the middle. What could be causing this? (photos)

this looks like localized morphea and needs a cosmetic dermatologist with expertise for improvement.  I suggest you see an expert.  Best, Dr. Emer.

As stated by the other physician in this forum you have pretty classic morphed-en coup de sabre. It is an autoimmune condition that is a localized variant of scleroderma. You should have an evaluation by a dermatologist with an interest in connective tissue diseases and autoimmune conditions. 

The picture is not of good quality.  Forehead veins can be treated safely and with excellent cosmetic results by either sclerotherapy, removal through tiny incisions or a combination of both.

Thank you for your question.The picture is poor quality but I see a vein left side of the picture (right forehead). It looks like a varicose vein.Manny options are available, some of which are microphlebectomy or sclerotherapy, among others.Best to see a vein specialist who has experience with these. Best,Dr. Karamanoukian