that one looks a lot more similar, but I would hesitate to say that the engraver modeled Septimius from Didius. Beard styles were similar, as most men at the time probably wore them, same as today with various styles that are copied. I have a beard and glasses and once had someone tell me I look like Stephen Spielberg; which superficially is true; but I was not modeled on him or vice versa, just coincidence. Also, Septimius portraits remain consistent through his coinage indicating a fairly reliable early portrait.