Non-melanomas are the most common form of skin cancer, and usually develop in the upper layers of the skin, and grow quite slowly. The first signs of non-melanoma cancers are often patches or lesions on the skin that refuse to heal, even after a few weeks. There are two types of non-melanoma cancers: basal cell carcinoma and squamous cell carcinoma, which start in either the top or bottom layers of the skin.
Example image of Basal Cell Carcinoma:
Example image of Squamous Cell Carcinoma: