Damn right the authorities can trace IP's. They can even identify Tor users now, apparently. 
 
In the case of a threat, the website they were issued through can be subpoenaed to reveal the details of anonymous users. Lots of people are being arrested for making threats over Twitter. They're total idiots.  

djwayne
Well I had pictures of my guitars, coin collection, vehicle, and my house which showed the address to a bunch of creepy people on another forum. They were able to identify me, my address, my phone number, e-mail address, luckily they haven't tried to steal my ID yet....all from pictures I innocently posted on my private library, I thought. They have threatened me, with physical violence, stealing my stuff, and vandalizing my vehicle and house. 
 
I posted one picture and that was all they needed to access my complete library. Photobucket opened the door for them to all kinds of information about me. 

I made my photbucket  libraries private …did you know that you can password your whole acct .
they do have that option (or did) a while back .
I did it for the same reason you are concerned about …
as far as I know …now when I post an image online that's the only image that will be seen .
good luck 
 
Kenny