Bill Egan’s email, cited in the last post, said that the sketch shown there is the only known extant image of Barney O’Sullivan. Thankfully, this is not the case, and there are several other pictures available.
One picture has very recently come to light: Philip Jurgens found a high quality photo in the Dutch National Archive of him in play against Szabó in the first round of the Hilversum Zonal in 1947.
(Click on photo to see a full screen version.)
The archive (Nederlands Nationaal Archief) link also has a higher resolution version of the photo.
The game was played on July 15, 1947. The photo was taken by D. Modriek. The caption translates to
The Hungarian Szabo (left); one of the favorites at the zonal tournament in his game against the Irishman O’Sullivan, who had to resign after only 21 moves [Western European Zonal Tournament in Hilversum]
Many thanks to Philip for pointing this out.