I don't know if the picture downloaded
Hi - the Minnie Mouse image looks like it's a printed image, probably applied to a piece of gum paste or fondant cut out to the same shape (to give it rigidity).
For the letters, you can just make your letters as usual and insert wires or toothpicks into the bottom as they're trying, then insert into the cake. Might want to use a little royal icing to help it stick.
Hope that helps!