stuffitall: "these people transpose pictures of kids they see onto all sorts of things"
That's just bogeyman stuff. Sure, there may be a very, very small number of people who do this, but to think that everyone who takes a child's picture is off to glue it onto porn is just daft. How many of "these people" do you think there are?
stuffitall: "taking pictures of strange children is not an innocent and kindly act"
What, never?
stuffitall: "what about a stranger offering your child sweets? that could be, to a child, "innocent and kindly"
You never know, maybe it is innocent and kindly. I have absolutely no problem at all with strangers talking to my son or offering him things (thanks for the pringles, student on the train last week). Since he's only 20m, we're always around. When he gets bigger the rule will be "Don't take things from strangers unless Mummy or Daddy is there".
"so instead of telling them not to talk to strangers, let's tell them not to talk to the most likely offenders, not to accept lifts from teachers, people they see around school, other people's fathers, youth group leaders... because they're more realistic offenders in terms of my child"
They are not the most likely offenders.
You. Are.
And the attitude you seem to be espousing - "Don't look at my child. Don't talk to my child. Keep away from my child." - is precisely the one which has led to numerous child deaths over the years, at the hands of their parents. Fred and Rosemary West's own children were kept away from strangers for very good reasons.