Well, the answer to that question is something I have been thinking about ever since launching Bazaarvoice with Brant. Why do people take the time to write reviews? [We will announce next week that we served over 19 million reviews on Cyber Monday!] Why do people take the time (like I did this morning) to vote on community photos for JPG Magazine? Why do people take the time to label images Google has crawled? [Google's top contributor, "wordgirl", has labeled 1,335,500 images since they launched this only three months ago - that is a staggering 14,839 images per day since launch!]

The answer is actually more complex than you may think. It is a combination of ego, social connection, and good karma. Let me explain:

1. Ego – At Bazaarvoice, we know that a reviewer comes back to our client's site three times, on average, after submitting a review to see if it has posted yet. When people take the time to share their opinion, they want to know the world heard it. This fact alone gives our clients three opportunities to resell a customer. In a recent report, Patti Freeman-Evans researched these reviewers.

2. Social connection – Why do you share your favorite movie with an acquaintance? Do you care if they watch it? Why do we talk about our favorite music? The answer is linked to human nature. We all care about connecting with each other as humans. This is what drives the creation of culture.

3. Good karma – A universal truth is that if you help someone, it makes you feel good. When reviewers help each other shop, it saves time. Saving time is one of the most important things we can help each other do, especially in the manic, multitasking world we live in today.

Now, if you apply these three elements to JPG Magazine, it all begins to make sense.

Obviously, we are thinking about the power of photos in customer-generated content at Bazaarvoice. A while back, we added Photo Reviews to our feature set. Wayne blogged about this recently. If you think about the three elements above, photos are a very strong component. Experts believe that the advent of the digital camera is one of the keys to why MySpace took off versus its predecessors (Geocities, etc).

How should you leverage photo reviews? With contests and multichannel recognition. Don't just run a contest for a gift certificate give-away for customers that write a review and include a photo, post the winning photo on your home page! Use it in an email campaign. Use it in a circular. Use it in an in-store display. If your community of customers sees that all three elements – ego, social connection, and good karma – are maximized by you, then it will spark customer participation unlike anything you have seen before. Threadless' entire business model is based on this, and I think it is a brilliant application of the three.

For fun, here is a photo we recently moderated that you won't see on one of our client's site because it came from a rejected review. Alas, it added no obvious value, there was no text review associated with it, and I think this person was just bored (they were thinking about element #1 above only – ego). But, it does grab your attention!