Bilberries are closely related to North American wild and cultivated blueberries and huckleberries in the genus Vaccinium. Some research shows bilberry (vaccinium myrtillis) to be effective as an antioxidant when ingested due to its antocyanin content. This effect has not been demonstrated on skin.
Bilberry extract is marketed as a hydroquinone alternative (like arbutin) for treating hyperpigmentation and sun damage due to its chemical composition, which includes botanical hydroquinone, vitamin A and vitamin C. Unfortunately, I can’t find any research that proves this ingredient works in this capacity.
Journal of Agricultural Food Chemistry, September 2001, pages 4183–4187