Right (Below/Right) - Illustrates a uniform pictured in Tunca Orses. Necmettin Ozcelik. (2007) Dunya Savasi'nda Turk Askeri Kiyafetleri 1914-1918. Militärmuseum, Istanbul: 35. Said to be from the Gallipoli Campaign, 1915. This seven-button sand-khaki cotton jacket with large gilt star and crescent buttons - identical to the Egypt Army, and the Turkish Army (the 1876 Button).
Right - First seen in 1908 various patterns of wide-brim sun hats were popular in the WW1 Ottoman army. The WW1 Turkish Army officer' wide-brim sunhat also came in a ‘soft version’, and due to the wide brim is often pictured with the fount brim folded up. This was to give the wearer unencumbered vision .
Right - Two versions of the post-1914 Turkish Army officer's sunhat, in the Imperial War Museum collection:
 Pictured in Tunca Orses. Necmettin Ozcelik. (2007) Dunya Savasi'nda Turk Askeri Kiyafetleri 1914-1918. Militärmuseum, Istanbul.
Right - Both these WW1 Turkish officers are wearing matching Austrian made kappenabzeichen as collar insignia, to distinguish the unit they belong too.
A: Is the 'Belgrad 1916' kappenabzeichen.
Below/Right - A Turkish junior officer wearing on the left side of the chest as a badge to distinguish the unit he belongs too. This is an Austrian made kappenabzeichen for XV.KAIS.OSM.ARMEE KORPS. For the XV Corps, Ottoman Imperial Army.
Austrian Army contractors made four kappenabzeichen for the Turkish Army Corps fighting in the East Europe Campaign in 1916-17.
The practice of soldiers of the Austria-Hungary army wearing the Kappenabzeichen (cap badges) largely began during WW I in 1914-1918. These served as unit emblem (as well as identified and commemorated specific events in the individual unit's war history), when the different troops were given the same field grey uniforms.
In the case of the Turkish troops, the Austrian Army extended the practice, to incorporate these soldiers as well. Four particular badges can be related to the XV Corps (Imperial Army):
XV.KAIS.OSM.ARMEE KORPS (Below/Right).
KAIS.OTTOM.15.KORPS.1916: This is also in gilt bronze stamped. With sewing loops on back. Marked on back: Gurschner Wien VII (Below).
GALIZIEN 1916 19.OTTOM.DIVISION: The 19th Ottoman Imperial Army Division, consisting of the 57th; 72nd; 77th Infantry Regiments. The 19th Division was commanded by Mustafa Kemal at Gallipoli. Zinc badge, with pin back. Maker marked on back: A G WINTER & ADLER WIEN.
HEERESGRUPPE BÖHM ERMOLLI (Battle of Kerensky, July 1917). Bronze gilt and enamelled. Unmarked.Böhm-Ermolli commanded the 2. Army from the beginning of the war (1914) till May 1918. This incorporated the Turkish XV. Corps, led by Generalmajor Javid Pasha. Atthe Battle of Kerensky, July 1917.