This trophy is unlocked by carrying the postcard stolen in the Shoplifting trophy all the way through the game and placing it back on the rack in the gift shop at the end.
The easiest way to do this is, as you work your way through the game, figure out where the challenge will end, typically by a locked door or collapsing bridge. Put the postcard down near this object and complete the challenge as normal. Then pick the postcard back up before leaving the area.
As long as one of your characters are holding the postcard you can use the save and quit option from the menu and you will still have it when you turn the game back on.
Glitch warning: DO NOT save and quit while holding the postcard on a ladder or rope. IT WILL DISAPPEAR and you will have to start a whole new playthrough.