Your assumption is correct.
The photographer is the owner of every photo that they have taken. Even if 2 people take an identical photograph, each photographer will own their own photograph. This includes popular tourist attractions which have their pictures taken several thousand times per day, the photographs may not be terribly unique, but each photo taken is still the property of it's photographer. The term of the copyright is from the time the photo was taken until the remainder of the year you die, plus 50 years.
That's Canadian law, I'm assuming there's something similar in American law.
If your photo is being used by a WordPress.COM user you should contact WordPress support staff. They're generally very good at sorting out copyright claims, if the person abusing your photos is on a hosted site try contacting the host directly.
"Character assassination" also counts as "defamation/libel". You may want to collect screenshots of the site for any later legal action.
If you're not doing so already I'd suggest keeping future photos at a low resolution when posting them to the web, and a smaller "height/width" ratio. It's also a really good idea to put some sort of watermark on them to identify your copyright claim.
Doing both gives you the automatic proof the photo copyright belongs to you, in case you have to prove the photo is yours.
This is the WP Copyright page:
This is where you contact Support:
And this is a free online watermark generator:
And this is the Blogger's Legal Guide regarding Intellectual Property:
Hope some of this helps.