There are now a number of good websites with information about butterflies. I consult these frequently and can wholeheartedly recommend them. Many of these sites contain large numbers of excellent photographs.
The Royal Photographic Society contains a number of specialist sub-groups including a very active Natural History Group. They organise regular fieldtrips throughout the year and are supportive of anybody with an interest in wildlife photography.
The RPS distinctions programme exists to encourage the development of photographic skills.
The Fédération International de l’Art Photographique is an international organisation linking national photographic associations throughout the world.
The Photographic Alliance of Great Britain is a membership organisation that co-ordinates activities for photographic clubs in the UK. It has strong links with the RPS and FIAP.
There are innumerable good websites on wildlife photography. I have only included those few that I visit regularly or whose authors I know personally.
Collins Butterfly Guide: The Most Complete Guide to the Butterflies of Britain and Europe. Tolman, T. and Lewington, R.
Butterflies: A Natural History (British Wildlife Collection). Martin Warren A definitive and readable text book covering all aspects of butterfly structure, life-cycles, behaviour and ecology.
Butterflies of Europe. Tristan Lafranchis
Papillons de France. Tristan Lafranchis
La Vie des Papillons. Tristan Lafranchis and others
Guide des Papillons de Jour et Zygènes des Pyrénées. Jude Lock and others. A really well-designed pocket book with all information clearly presented. Perfect for identifying all the butterflies (and Burnet moths) to be found in the Pyrenees.
Close-up and Macrophotography. Robert Thompson
Life Cycles of British and Irish Butterflies by Peter Eeles. (2019) Pisces Publications, Berkshire. ISBN 979-1-874357-88-9. This is a truly wonderful book based on many years of diligent work rearing and photographing each stage of every species.