Poll: Which is a better storage method?

So I am in the process of coding up a new site with MySQL/PHP … The site will be storing a large number of photos. I am wondering which method would be the best to store the data with. Currently the images are getting uploaded in a raw format, but are going to be resized and store a total of 3 version + a thumbnail. I am trying to plan ahead on the site and assume that it will draw a large bit of traffic and could eventually need to be balanced between a few machines (Yes I know I am thinking big here). But for performance purposes would storing the images as flat files or in a database be a better idea? Let me know what you think, and why. Thanks
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