I know some very frum people who have facebook. Some of these people are into Kiruv. So I assume that’s a good way for them to keep in touch with the ppl they are being mekarev. I don’t doubt that their fb accounts are totally clean and kosher.
As far as posting pics, who says you have to? You can have an account with no pics at all.
I personally think it depends on how you use it. If you’re just keeping in touch and only have appropriate things on there, why should that be a problem?
I will give one VERY IMPORTANT warning- IT IS VERY POSSIBLE TO HAVE YOUR ACCOUNT HACKED AND INAPPROPRIATE THINGS CAN/WILL SHOW UP ON YOUR PROFILE. I know someone who had that happen. So, if you’re going to have an account, you should have your fb friends let u know if they see anything wrong. You may not be able to see it yourself. I don’t know how that works but it is possible for you not to see what others do on your own account.