I am looking to ID country, rank, and unit shown in this picture.
I have already tried googling the collar insignia with no luck.
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This is definitely an officers uniform of the 1st French foreign legion regiment due to the collar patch with a "1" in the hollowed out grenade though I believe he is wearing the British style "new tunic" which was introduced in spring 1915 for Officers though this was unpopular in the Army except for its Aviation Branch.
Example of the collar patch from "The French army in the first world war uniforms and equipment volume 2 - Laurent Mirouze"