What is the Islamic ruling on posting personal photos (especially for girls) on social networking sites like Facebook when these pictures might be seen and commented on?

In the Name of Allah, the Beneficent, the Merciful,

All praise is due to Allah, and may peace and blessing be upon the Messenger of Allah, upon his household, his companions and those who have followed him. To proceed:

Putting up personal photos on public sites like this is not permissible for those who fear Allah, since this is an occasion for others to be tempted by her and an opening to have an excuse to contact her. It breaks down the barriers of modesty between the sexes, and most fires are from the smallest of sparks. Therefore, we advise our sisters to stop doing that and to remember always that this culture is a foreign import; it has no relation to our culture, nor does it fit within our values.

We ask Allah to guide everyone.

And Allah Almighty is the Most High, and He knows best.