Yes, I see that raised "ridge" which
may indicate a strip of tape on the joint seam
underneath the final fabric covering of the fuselage.
There was another picture in the "Pfalz Aircraft of WWI" book (page 38), which shows D.III on its nose from a bottom view, in which the joint line appears to be
very dark and obvious (much like a built model that was not sanded or smoothed down).
I did not see anything else in the text regarding details on how the joint lines were dealt with.
Mr. Dan-San, help please....
