There’s no tap dancing around it, iPhone photo app Camera+ is a money-making machine.

The sophisticated photo capture and edit application, built by iOS development shop Tap Tap Tap, has been purchased more than 6 million times on the App Store. Camera+ has also made its makers $5.1 million in revenue to date, company principal John Casasanta revealed Friday.

Camera+, which currently retails for $0.99 and offers for-charge in-app upgrades, has been a consistently strong performer on the App Store, even as the free one-touch filter application Instagram has skyrocketed to Internet stardom.

The app appeals to a growing crop of iPhoneographers in search of robust mobile photo-editing tools, and sales have climbed as the iPhone’s camera quality has improved. The launch of Apple’s iPhone 4S device and the increased app interest during the recent holiday season have propelled sales to an all-time high.

“Both were increases that were expected but what’s been surprising is how long each has lasted,” Casasanta said. “When the iPhone 4S came out, Camera+ sales have approximately doubled and have sustained that new level since then. And with Christmas, even though it occurred weeks ago, sales have increased by about 2/3 more than the level they were before the holiday.”

All signs are pointing to continued success: Camera+ had almost 1 million sales in the past 30 days alone, and it’s now selling at an average rate of one application every three seconds.

Camera+, which is heavy on effects and editing tools and light on social features, seems to have found a winning strategy for making money on the App Store. Instagram meanwhile, also a hit iPhone-only photo application, continues to sign up new members at an increasing rate (Instagram has about 10 million more users than Camera+), but has no real revenues to speak of. The applications are more complimentary than they are competitive, but it’s interesting to watch as two similarly-purposed applications take off and travel down distinct paths.

[Image via Tap Tap Tap]