Between 1970 and 1992 I turned over around $3million in fees for commissioned photographs but during that time I rarely got much of a fee for a picture that already existed. I got paid for creating the picture that previously had not existed. The advent of computer-retouching meant that me skills were no longer needed and I went into the diving industry and used my photographs to support my writing. Despite retiring from actively being a diving journalist I still get requests to use my pictures in return for a credit only but feel that at my time of life a photo credit doesn't contribute to my pension! Since then, it has become so easy to get good pictures underwater that very few are 'special'. In recent years, even if I was the first to shoot some subject, very soon the world and his wife were doing the same. So the only use I can see for my pictures now is to illustrate any books I choose to author - and the writing had better be top quality!
So enjoy taking pictures but consider yourself the only client. You can give away their usage but remember, as NYC photographer Lou Long would have said, "If it's free, it ain't worth nuthin', kid!"