Greenie questions...sorry (apologies in advance)

Hi All, Just a few questions from a totally uninformed, no knowledge newbie. Say for example one wanted to be just an extra, purely an extra and didnt have designs or dreams of anything more than being wallpaper or blending in to the background for a bit of extra cash. Would one really be required to have 30-60 headshots (seems excessive for just an extra position)? Perhaps it is so, I certainly wouldnt know as I havent any real idea of what this industry requires, though I am hoping someone here might be able to give me some further clarification on these things. Also there seems to be a lot of furor over agencies, if one wanted work as JUST an extra which would be the best for this relatively small role (I am assuming there wouldnt be a huge amount of work required to promote an extra, just a basic profile and maybe one pic right?). Surely there wouldnt be an exorbitant fee for this type of service only a commission on any work undertaken? Any advice or inputs of knowledge much welcomed and appreciated, Wishing you a chocolatey Easter, Miss Darcy (the wannabe wallflower)