In a blender, combine thawed blueberries, lime juice, and icing sugar, and blend until smooth. Set aside.
In a small bowl, combine gelatin and water. Let gelatin bloom for 5 minutes. Meanwhile, bring a shallow pan of water to a simmer. Place the small bowl over the simmering water and mix until gelatin has liquified.
In another bowl, combine graham cracker crumbs and melted butter. Press mixture in the base of a 6-inch spring form pan. Refrigerate the base for 30 minutes until firm.
When ready to serve, run a knife under hot running water, dry it and carefully run it around the inside perimeter of the cake. Remove the metal ring around the cake. Garnish with fresh blueberries or cake toppers of choice.