Based on the real ones!
(Which are now only reproductions, obviously...)
What's sad is that in 1977 Jean Clottes (who studied these drawings) warned people about the degradations, but didn't know what to do about it. Had someone put a grill at the entrance or a frame around the drawings, it would have excite curiosity. Back in the days there was no reglementations around caves... So basically anyone willing to could enter and draw whatever they want on walls. Sorry for the long post!