If you say so. Good luck with that.
No he is correct. Whenever you take a photo or create artwork you do own a copyright on that work. While its true most online image hosting services do ask you to give them the rights to display your work you are not giving up your ownership of that work but are merely giving them the right to show it. Typically this only becomes an issue in court cases where art is used for commercial purposes or in a defamation case.
For example the most common use I see are photographers. They often watermark the photo proofs they send to clients so they can pick and choose which ones they'd like to order. By sending the client those photo proofs they are not giving up ownership of those images for print or web distribution (about half my facebook newsfeed I'm looking at you). Most photographers charge extra to get the rights to their work and thats why if you look on the back of most professional photos they have the photographers contact information. Another example is sports photography, KSR was threatened with a lawsuit for using unlicensed images on its ad supported commercial blog by increasingly irrelevant print newspapers.
Now all of this likely would not apply to posting someones family pics in a message board thread, that I just feel is bad karma but is just to illustrate that technically you don't give up the rights to your image because you uploaded it to the internet.