How can the indentation on my forehead be treated? (photo)

The photo suggests the presence of one forehead indentation. If this represents an indented or depressed scar subsequent to trauma to the area, then subcision with or without the addition of a volumizing filler would be an easy and viable option for treating the condition. However, if there is no prior history of trauma, infection or inflammatory process, the underlying cause must be determined and addressed before embarking on any aesthetic treatments. Consultation with a board certified dermatologist is highly recommended. Once more serious medical conditions have been ruled out, subcision might be considered for treating the indentation. For over twenty years, subcision has proven an easy and effective method for permanently elevating depressed scars of various types. Subcision is a procedure in which a sterilized needle is inserted, following the administration of local anesthesia, directly beneath a depressed scar (regardless of whether from acne, infection, trauma, or surgery) and used to break up the thick bands of fibrous scar tissue that bind down the surface and create the depression. On a small, linear scar, such as this, treatment would likely take no more than a couple of minutes.Breaking up the abnormal bands of thickened, scar collagen accomplishes two things. First, it allows the surface of the scar to float to the surface. In addition, the tissue fluid that immediately fills the space following treatment contains growth factors and other wound healing substances that promote neocollagenesis, native collagen production, that allows for improvement and elevation of the scars. Between two to four treatments, spaced at six week intervals, are generally required to promote sufficient new collagen to achieve a satisfactory improvement. Since, the collagen produced is one's own, the results of subcision are typically permanent. To further plump the depression and stimulate additional collagen production, a small amount of volumizer filler, such as Radiesse or Radiesse combined with Perlane L may be injected immediately following subcision treatment or between treatment sessions. 

Fillers are usually used rather than Botox to raise indentations to make them more even with the rest of your skin. However, a physical exam would be required to determine if this would be effective or another treatment.

It is most important that you find out what is causing indents on your forehead.  If you had trauma then that can explain it.  However indents spontaneously forming on your forehead could indicate an underlying skin problem.If the indents is the result of trauma thin filler injections with Perlane or Juvederm could help.