uhlans

The caption actually read "Uhlan Prisoners" not "German prisoners". Uhlans are a type light cavalry.

Douai is a commune in the Nord département in northern France, very near Belgium, in the path of the German invasion in 1914.
en.wikipedia.org/wiki/Douai
In this photo, two rows of French cavalry, with unarmed Germans walking between.
Similarly dressed French cavalrymen:

bior: Thanks for pointing out the correct caption. We'll fix it next time we update the description.

Agence Meurisse photo on Gallica site, publ. 1914, with caption: "Uhlans faits prisonniers près de Douai" gallica.bnf.fr/ark:/12148/btv1b9041508r

From Wiki Uhlans (in Polish: "Ułan"; "Ulan" in German) were Polish light cavalry armed with lances, sabres and pistols. The title was later used by lancer regiments in the Russian, Prussian, and Austrian armies. Uhlans typically wore a double-breasted jacket (kurta) with a coloured panel (plastron) at the front, a coloured sash, and a square-topped Polish lancer cap (czapka) also spelt 'chapka,' chapska and schapska. This cap or cavalry helmet was derived from a traditional design of Polish cap, made more formal and stylised for military use. Their lances usually had small, swallow-tailed flags (known as the lance pennon) just below the spearhead.

en.wikipedia.org/wiki/Wilhelm,_German_Crown_Prince
"Wilhelm, German Crown Prince, Crown Prince of Prussia (Friedrich Wilhelm Victor August Ernst; 6 May 1882 – 20 July 1951), was the eldest child of the last German emperor, Wilhelm II, and his consort Augusta Victoria of Schleswig-Holstein. As Emperor Wilhelm's heir, he was the last German Crown Prince and Crown Prince of Prussia, until the abolition of the monarchy."
He married Duchess Cecilie of Mecklenburg-Schwerin in 1905.
See her at

Uhlans (in Polish: "Ułan"; "Ulan" in German) were Polish light cavalry armed with lances, sabres and pistols. The title was later used by lancer regiments in the Russian, Prussian, and Austrian armies. Uhlans typically wore a double-breasted jacket (kurta) with a coloured panel (plastron) at the front, a coloured sash, and a square-topped Polish lancer cap (czapka) also spelt 'chapka,' chapska and schapska. This cap or cavalry helmet was derived from a traditional design of Polish cap, made more formal and stylised for military use. Their lances usually had small, swallow-tailed flags (known as the lance pennon) just below the spearhead. en.wikipedia.org/wiki/Uhlan On Guelzin I find Le Port Ecluse Guelzin, which leads me to Condé-sur-l'Escaut: Condé-sur-l'Escaut is a commune of the Nord department in northern France. It lies on the border with Belgium. The population in 1999 was 10,527. en.wikipedia.org/wiki/Condé-sur-l'Escaut An alternative is Gœulzin: Gœulzin is a commune in the Nord department in northern France. en.wikipedia.org/wiki/Gœulzin Both are on the Belgian border, so both likely saw action in the early stages of the war.

I didn't know they still used lances in WWI. They would have been no match for those rifles, probably bolt-action, possibly Enfields. I assume the captors would be British or French but can't find a match for the uniform.

I think that's French cavalry guarding the prisoners. You can see those odd helmets in this wiki photo: en.wikipedia.org/wiki/File:French_heavy_cavalry_Paris_Aug...

I couldn't find out much about the helmets. They may be Tarleton style, which were made of leather and used by the French army since medieval times. The French introduced the first steel combat helmet in 1915 but it wasn't issued to the cavalry.

These are French Dragons.