It isn't very easy to crack down on this. New members might be legitimate and may also have good points to contribute as either a thread or a post. You never know when a troll could easily make a new account, regardless if they're using Tor or not.
The probable solution would be this:
1. Allow images to be posted after X amount of posts
2. Allow thread making after X amount of posts and/or likes and posts.
3. Implement a reminder system, similar to what Andreas posted earlier. An automated message that comes in along with the verification email, reminding you that certain features will be disabled until the user is given the "thumbs up" and is allowed to post freely, images and topic speaking.
The only problem is, there would still be trolls boosting their reputation up to earn those features and to completely spam out troll threads and images.
While not a logical option, those mentioned above could temporarily solve the troll issue.