You can find a bigger version of the voodoo image on the Scumm Bar
and possibly MixnMojo
. It's not concept art as such, but rather the original artwork for the scene before it was compressed into 1991 quality. Tragically, every scene in the game was drawn with quality like that but only two (Captain Dread's shore and the voodoo house) were released.
The art on the left is a custom piece of art that was made specially for this forum a few years ago by Dan Lee. He also illustrated the first two headers for MixnMojo's 'Secret History' article series:
Whereas the latest one posted yesterday was illustrated by Paco Vink:
All can be clicked for big versions.
I'm sure they'll appreciate a kind comment on the articles.