A veneer mainly covers the front surface of a tooth and is used for cosmetic improvement when enough healthy tooth structure remains. A crown covers more of the tooth and is used when the tooth needs stronger protection or has larger damage.
Crowns may be recommended for heavily filled, cracked, root-canal-treated, or structurally weak teeth. Veneers are usually more conservative for suitable front teeth. The dentist will advise which option fits your tooth condition, not only the appearance.