There are several ways it could be done, one method would be to machine the whole work piece using the material as a boundary, easy to do but the downside is the finish quality on the flat areas of the lid & the time taken to machine it all using 3D toolpaths. Another method would be to use a vector boundary & just machine the rose using 3D toolpaths & then pocket the rest of the lid down to the required depth. Quicker method but requires a bit more accuracy setting up to ensure you don't get a step where the 2 meet
There are quite a few tutorials on 3D machining & also some tutorials on efficient 3D machining in the 2015 user group section
I do the pocket like Martin said around the outer periphery of the model boundary.
Just a little tweak though. What I do is create the material boundary then painstakingly node edit to get the boundary as smooth as possible and as few nodes as possible. Then I offset "IN" a few thousandths - maybe .01 or so.
Also - I set the pocket deeper than the model, so that there is a little bit of straight sides on the outer periphery of the model.
By doing this I get a nice flat surface of the outer pocket area right up to the model with no step. Nice clean look.