Books for badges
All the recommended books for badge collecting and identification appear to be out of print. Your library might be able to obtain a copy of this book which has line drawings of all British Army Cap Badges:
EDWARDS, TJ. 1981. Regimental Badges. ISBN 0510000835: Benn.
Alternatives include this one with photographs of thousands of First World War badges:
COX, RHW. 1982. Military Badges of the British Empire 1914-18. ISBN 0510000827: Naval and Military Press.
Or try to find:
KIPLING, AL and KING, HL. 1995. Head-Dress Badges of the British Army - Volume 1 - Up to the end of the Great War. ISBN 0584109474: Muller, Blond and White Ltd.