Chance of you being jailed for it: above average. Chance that anyone will be helped by you turning it in: far below average. Take your chances, if you dare.
Doing anything to cover yourself, such as sending it to the cops through the mail anonymously will further raise the chances that the cops will try to pin it on you.
Because depending on exactly what is on that card there may be a child in real pain?
Maybe it's old photos, but if it's recent stuff you can actually help someone.