The image of Cosette used for the iconic logo of the Les Misérables musical is based on an etching by Gustave Brion, which is in turn from an illustration by Émile Bayard (1837–1891) for the first edition of the book. Dewynters creative director Russ Eglin adopted the art for the 1985 London production logo, pairing it with Caslon Antique. (Eglin went on to design for other Cameron Mackintosh productions such as The Phantom of the Opera and Cats.)
As vital as the Cosette image is to the franchise, the logotype may be even more so, having survived for several decades, even up to the recent Hollywood film in which the classic illustration is replaced by a photo of the actor playing Cosette.
The Les Misérables logo is almost certainly the most famous modern use of Caslon Antique, a typeface by Bernd Nadall that was released in metal by Barnhart Brothers & Spindler way back in the late 1800s. The design has nothing to do with Caslon which was likely applied for marketing reasons more than anything. The various digital interpretations of Caslon Antique vary widely, probably because they used different sizes as their sources, but also because some versions appear to smooth out a few of the original’s rough contours.