origin of the Our Lady of Grace statues?

[Geremia]

What is the original Our Lady of Grace statue? Is it associated with a particular Marian apparition?
There are many coloration variations in these statues, so I show this monochrome garden statue as an example:

All the "Our Lady of Grace" ones show her in this posture—open palms, downcast eyes, and stepping on the serpent.

[Geremia]

 The origin of the statue is actually the medal of Our Lady of the Miraculous Medal, in which the Blessed Virgin appeared to St. Catherine Labouré in 1830 and told her to make a medal according to her specifications:

From St. Catherine Labouré's biography, the Blessed Virgin Mother said:

"Have a Medal struck after this model. All who wear it will receive great graces; they should wear it around the neck. Graces will abound for persons who wear it with confidence."

This would explain why she is also called "Our Lady of Grace".