I now make sure all our family photos are anotated on the back as yout right it is so frustrating to have all these photos and have no way of finding out more info about them.
Will copy some of my grandads photos etc and post them, a few years ago i was lucky enough to get a couple of guys to go to Kew and they found my Grandads records and produced a nice brochure for me with them in , it only cost £30 , one of the best 30 quids i've spent, i learnt more about him through them than i could have found out in a lifetime !!
I have a cracking 18 pounder shell from Thiepval on the Somme which i will photograph then post.
It is highly likely that your Grandfather will have fought all over the Western Front in all the major Battlefields due to the way in which the Artillery units were moved around. I have been to the Firepower Museum at Woolwich aa they have the Artillery war diaries and i now have the war diaries for both Batteries so know exactly where he was at any one time , they may be able to pin down your grandfathers exact unit for you
all the best