Is this an accurate depiction of the internal shape of a turbofan engine?
Strictly speaking, no. It is an artist's concept to help us understand the engine schematics better. A better figure would look some thing like this :



GE-90 Cutaway; image from web.stanford.edu

The blue colored region more or less shows the 'cold flow' region (where the bypass air flows). This graphic is better for two reasons- not only does it show that much of the flow takes place in the cold flow half-ducts, but it also shows that how the pipes and tubes that are all over the place are covered.

The figure you linked in the question doesn't show the cold air flow ducts, for simplification. Also, the shape and size of the bypass duct varies from design to design (though they are similar overall).



Differences between two and three shaft engines; image from 1.bp.blogspot.com

In the above figure, you can see that the though both the similarly shaped bypass ducts converge, their location and length is different. Of course, in the real aircraft, these ducts host the thrust reversers, as explained by @mins elsewhere.