What is the legality of a company copyrighting a picture that i uploaded onto facebook?

[bcnu]

You took the picture originally? That makes you the copyright owner automatically. That is the US copyright law and similar in over 160 countries that follow the Berne Convention. On the other hand, if you didn't personally make the original photo, then you have no rights to it at all. Let's assume you personally snapped the photo yourself.

You posted your copyrighted photo on FB which only gives FB users a limited license to DISPLAY that photo, not to publish it anywhere else.

You still own the copyright. You can only TRANSFER your copyright by signing a document that says you intend to transfer your copyright. Someone saying you somehow lose your copyright when "it's out there" is simply wrong.

You can immediately contact any website that is publishing your copyrighted photo without your permission and simply ask them to remove the infringement immediately. They must legally do so "promptly". 17 USC § 512. You can register your copyright and sue anyone who continues to violation your rights.

As for @Norm's answer, it is completely false and there is no possible way a person who is ACTUALLY a paralegal would completely misstate the most fundamental rule of copyright: YOU OWN IT AUTOMATICALLY. You have only LICENSED it to FB. Perhaps "Norm" is still reading the copyright law from over 20 years ago.

17 USC § 201 Ownership by author.
17 USC § 1202 Unlawful to falsely claim copyright ownership or remove copyright notice of others
17 USC Chapter 4, Copyright notice optional, registration of copyright optional until (§ 411) you want to sue in US federal courts.