What’s the difference between MeshCAM Standard and Art?

The only difference between Art and Standard is the image-to-relief functions in MeshCAM Art. A quick video showing this feature in action can be found here

Note that MeshCAM Standard is still able to load image files as a height map but it gives you no control over the shapes applied to the image.

Do I need to buy MeshCAM Standard if I own Art

Absolutely not- MeshCAM Art contains all of the machining functionality contained in Standard plus the 3D relief features outlined above.