On the back:

Jesus said to Saint Faustina:

"I am offering people a vessel with which they are to keep coming for graces to the fountain of mercy. That vessel is this image with the signature: 'Jesus, I trust in You.' "

"I promise that the soul that will venerate this image will not perish. I also promise victory over (its) enemies already here on earth, especially at the hour of death. I Myself will defend it as My own glory."

Taken from the Diary of Saint Faustina, Ref 327, 48, 326.