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The picture of the Grand Fleet came from this picture:
As for the other ones - I presume you're talking about the ones on the title screen - I'm not sure. The two on the bottom-right come from film footage, the first a widely used one of British soldiers going 'over the top' at the Somme in 1916, and the other of Field Marshal French inspecting British troops in 1914. The other ones presumably were found after some Googling.
If I remember rightly, that is indeed where I found the majority of the original pictures for the title screen. (Not to mention most of the contemporary photos I've used in my AAR. Strangely enough, WW1 pictures seem to be much easier to find on the Web than WW2 ones)