Well, apparently it could be either, but I'm not quite understanding what the distinction between "originel" and "original" might be.
WordReference says that "originel" specifically means "first", but surely that's what "original" means as well, in French or English.
Francophones, please elucidate.
Later edit: Upon further research, I'm getting the idea that "originel" is a less-frequently-used word, except in certain stock phrases ("le péché originel" = "original sin"), and it seems to refer generally to really old stuff - things from the earliest beginnings of whatever we're talking about. We might translate it as "primordial", perhaps.
Originale (plural originaux) means that it comes directly from the author, it is the first source of reproductions. Original means also unique or out of common.
-J'ai offert un cadeau original
However, originel means it comes from the origin. In a religious context, it goes back to the creation, to the first man created by God. We have also the expression the original sin