What caused this indent on the lower edge of my eye? (Photo)

There are a few different things that could cause an indentation in your eyelid margin.  At this point you should have it examined my an ophthalmologist or oculoplastic surgeon to rule out the possibility of skin cancer.  Depending on your age and risks factors, it may warrant a biopsy or simply be followed.

I do see the area of your concern. You do not give a history of trauma or infection, or how long this has been present, so it is difficult to prognosticate. I would see an ophthalmologist if your family doctor is unsure of diagnosis (assuming you were not born with this condition).    It could be something that would respond to simple treatment (like antibiotics if you had an infection, or massage of the lid if it is some post-traumatic scarring), but you need to have an expert examine you.