The sketch in question
While pictures circulate from time to time that are identified as Stirner, each one that I have encountered has been proven to be someone else. There are, for example, pictures of Marc Bloch and Rudolph Steiner that have been falsely identified as Stirner. Once these misidentified photos have circulated online, of course, it become more difficult to correct the mistake. In a similar case, photos of Imre Madách and Ravachol have been identified as the anarchist Joseph Déjacque and even a fairly concerted effort to correct the errors hasn't stopped the photos showing up as genuine in places where people would be expected to know better.