The following statistics came from a reddit AMA from the creator of Imgur. They're taken from a month in 2013. The advertising revenue pays for the 4.10 PB of data transferred.

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Site stats in the past 30 days according to Google Analytics:
• Visits: 205,670,059
• Unique Visitors: 45,046,495
• Pageviews: 2,313,286,251
• Pages / Visit: 11.25
• Avg. Visit Duration: 00:11:14
• Bounce Rate: 35.31%
• % New Visits: 17.05%
Infrastructure stats over the past 30 days according to our own data and our CDN:
• Data Transferred: 4.10 PB
• Uploaded Images: 20,518,559
• Image Views: 33,333,452,172
• Average Image Size: 198.84 KB

From <https://www.reddit.com/r/IAmA/comments/y81ju/i_created_imgur_ama/>;