Here it is!
Photo taken from the safety of a trench just above the parapet, showing us the desolated and corpse filled no man's land in the dunes at the 'Seekessel', (which was the last German position before the frontline ends at the North Sea), after the failed German attack on May 9th, 1915, where the Germans launched a large scale attack on nearly all subsectors within the Seafront sector. During this attack the Germans would lose an estimated 1200 men (wounded, dead, captured).
Many thanks to Utgardloki and Bayern for transcribing the text on the back of the photo, so we finally have the extra info for this photo.
"Seestellung in den Dunen.
Blick auf das Leichenfeld (Seesoldaten) vom
Sturmangriff am 9. Mai 1915."
Loosely translates to:
"Sea position in the Dunes.
View of the corpse field (Marines) from
the assault on 9. May 1915."
"(Seesoldaten)" must be an Indication that the corpses we see in this photo, belong to either the 'See Bataillon' or the 'Matrosen Division' units.