You can do some charity for your fans some times, especially during events that mean so much to them. You can publish their birthday party pictures, wedding pictures or anniversaries. This will create a bond between you as a blogger and the readers. They will likely never forget your blog when you do this.
You can also request for pictures yourself from people for contest or challenge. For example, you may decide to put all the pictures in a post and number them, and then ask the fans to guess a name for each person. The reader with the highest success rate wins.
The content you accept could also be event witnessed by a popular reader of your blog, and remember to say that a fan sent it in while posting. That’s how some bloggers are able t publish fresh and original materials even when they live miles away from where an event occurred.
Just let your readers know that they can actually send in events happening around them for you. CNN has this ireporter where they do this same thing.