Hey there,
Sorry to hear your beautiful betta is unwell, Growths on the fins don't usually affect the health of the betta unless it grows and reaches the body. I once had a betta that had a rare type of tumor on his anal fin, a good friend of mine who is pretty much a fish vet opperated on him and removed the weird looking tumor that looked like a bunch of grapes, my betta fully recovered and was fine. Does your boy have any other symptoms of illness? I am sorry I could not be of more help, does your camera have a macro setting? if so activate it when you take a pic of your boy because macro is great for showing fine detail, good luck and let me know how he goes