All fungal nail infections are known by the name onychomycosis. Fungal infections are less common on the fingernails than on the toenails, where they are sometimes accompanied by athlete's foot, a fungal infection caused by ringworm and occurring between the toes, as the Centers for Disease Control and Prevention explains.
Photos of nail fungus on the toenails and fingernails are available from the CDC and at MedicineNet. Infected nails often appear cracked, yellow, thick and fragile. Diabetics and people with weakened immune system disorders are most likely to contract nail fungus. Nail fungus is difficult to treat and typically requires oral antifungal medication, according to the CDC. In some extreme cases, the affected nail may have to be removed.