During earlier years before lenses actually focused to life size magnification, an image was considered macro when the subject was the same size as in life when it was printed on a 4X5 photo. This was because most lenses only focused to close distances of a few feet.

However, with the advances in lens design, lenses now focus within inches of their subject, so a macro image is considered "true macro" when the subject is the same size (or larger) on a 35mm full frame (24x36mm) as it is in real life. Anything less than 1:1 magnification is considered "Close Up". And while this probably isn't going to win me any friends, it needs to be said: Cropping an image of less than 1:1 does not make it macro. While there are circumstances where cropping is needed, such as when having a circular frame if using a reversed lens, or to help composition... there are several things to consider before cropping your shots.