My first thought was exhaust pipe, but there are other odd looking features that show up when you play with the contrast.
However, Der Grune Flieger basically got it as a Krieger Eindecker, but Dave got which one (I think that is the proper designation, but mostly I just see 1915 eindecker). There must have been more than one Krieger Eindecker, as it is reported that Krieger got his pilot's licence in 1911 on an eindecker that he had built. I have not been able to find out anything about spacifications or performance of this machine, or about other Krieger machines, so if anyone has information I would be interested.
So far as points are concerned, I will give Phil .8; Dave .2.
Current scores are:
35.3 Varese2002
20.5 Dave_Kent
15.5 Rbailey
9.3 Rod Filan
8.3 YavorD
7.4 JohnMacG
7.0 Breguet
5.9 Cruze
6.1 joegertler
6.0 Eric Goedkoop
5.6 ercoupepilot
5.5 EdStevens
5.4 Colin A. Owers
4.4 Ross Moorhouse
4.3 edmondthieffry
4.1 bshatzer
4 greenknight
4 Gilles
3.7 dpolglaze
2.7 Berman
2 Tom L
1.4 FOKKERJ
1.2 Ransom E. Olds
1 Peter Zambori
1 Gregoire
1.8 Der Grune Flieger
1 cubsfan4life
1 austin08
1 Cliff
.8 Machinbird
.6 Crankcase
.4 Vilkata
.2 Paul_J._Fisher
Previous challenges are on
http://www.earlyaviator.com/br.challenge/
Next one come soon.