A Pigeon or a Dove? What's the difference?

I can't really differentiate a dove from a pigeon... Specially if the bird is white in color.

Per Ask.Com: "According to Global Britannica, although the terms dove and pigeon are often used interchangeably, there are differences between the two species. Doves typically have smaller bodies and bigger tails than pigeons. But there is an exception: the domestic pigeon, which is often called a rock dove and also known as the "dove of peace." Pigeons and doves belong to the same family, Columbidae, and have many similar features."