Right - The white beaded senior officer is actually Sultan Mehmed V Reshad, in his post 1909 Dress Uniform (which is the first time that a specific rank was created for the Sultan in the Imperial Army.
Next to him is an officer called "Leibwache des Sultan" (Bodyguard of the Sultan). This was his personal imperial security detail.
Behind, is a group of mounted lancers called the "Leibgarde-Kavallerie-Regiment" "Ertogrul", which is actually the former - Ertugrul Cavalry Regiment of the Imperial Guard (pre-1908).
The award of the 1876 "Honorary Aide-de-camp to His Majesty Sultan", aiguillette continued after 1908, and in 1918-19, Mustafa Kemal Pasha writes in his memoir that the importance of his position, and his status as the "Hero of Anafartalar" after the Gallipoli Campaign, and his title of Fahri Yaver-i Hazret-i Şehriyari ("Honorary Aide-de-camp to His Majesty Sultan") gave him credentials in is campaign.
Right - Post-1909 "Honorary Aide-de-camp to His Majesty Sultan" versions of the aiguillette used into WW1, were designed as massive insignia, that cover the whole right chest of the wearer. These later versions, have five cords that come out from the right (facing) of this shoulder attachment. In particular, the quite visible two single cords that completely encircle the wearer’s right arm.
 The special rank insignia for Sultan Mehmed V Reshad (ruling from 27 April 1909 – 3 July 1918), was a badge based on his ‘Tugra’ (the imperial cipher, and symbol of authority).
Right - A wartime picture of an officer in the Sultan’s Palace Company, wearing a high quality post-1909 red uniform.
The Palace Guards wore 1909 White cloth and cotton tape dress epaulette identical to the version used by the police. The British General Staff. (1995) 1916 Handbook of the Turkish Army. Battery Press (Nashville), states:
Below - A parade of the Sultan’s Palace Company, wearing a high quality post-1909 red uniform,
Right - In 1909 the re-incorporated Ertugrul cavalry had became the basis for the newly formed Sultan's Guard Cavalry Escorts.
Right - Another 1908 illustration of the Sultan's Guard Cavalry Escorts (which were the former Ertugrul Cavalry).
Right - Displayed in the Turkish National Army Museum a Sultan's escorts uniform. The British General Staff. (1995) 1916 Handbook of the Turkish Army. Battery Press (Nashville), states: "The Bodyguard Squadron are clothed in crimson pantaloons and jacket, and while kalpak with red top" (p.63). However, this appears to be a confusion with the Sultan's Bodyguard uniform. As well, the dress uniform of the "1st (Lancer) Regiment" ... [is described as] ... "dark blue tunic with scarlet collar and cuffs: black kalpak, with black bag and silver stripes" (p.63).
Right - Two officers in the Sultant's escorts. It is not entirely clear, if these Sultan's Guard Cavalry Escorts, are the same unit as the former Ertugrul Cavalry (discussed above), or a completely separate unit. They are wearing post-1909 Army Officer's brocade belts.
Below - A mounted parade of the Sultan's Mounted Escorts prior to WW1.
Right - Displayed in the Turkish National Army Museum, a high quality example of an Imperial Gendarmes officer's uniform, from after 1909. Note, in particular the imperial sunbust badge on the collar. This is either:
This uniform uses the pre-1908 Gendarme officer's rank insignia (discussed above). This is the gold/silver cord chevron, under the gold triple cuff knot (which also incorporates an imperial sunbust badge inside the top knot):
Right - A pre-WW1 picture of an Imperial Gendarme, wearing the same uniform as that displayed in the Turkish National Army Museum (above), combined with a 1860s period Ottoman busby:headgear.
Below/Right - Imperial Gendarmes pictured, they wear a Light Blue or Red collar patch - reflecting pre- and post-1916 uniform collar changes.
Right - The collar patch displays the Ottoman Imperial sunburst with a five-point star, or the oval badge with the Sultan's Tugra.
As can be seen the shoulder boards are either for a ‘Bascavus Muavini’ (Assistant Sergeant-major, with two gold bars across the shoulder board), or a Cavus (Sergeant, with one gold bar across the shoulder board).
These shoulder boards are also coloured Light Blue or Red, to match the collar patch.
Maison Militaire de S.M. Imperiale le Sultan Mehmed V Reshad Corps des Pages at the Topkapı Palace School were selected from the Ottoman Boy Scouts in WW1.