Do you know how to init ov7670?
In addition to the information in the basic data sheet there is information provided in their document "Serial Camera Control Bus functional specification" 

Here -  Omnivision Technologies - Serial Camera Control Bus - SCCB functional specification 

Here is a two page product brief for your module. Useful in that it shows an envisaged application. VGA x 30 fps capable. OV7670 vga Product Brief .
 Some text from this product brief at end of this post.  

While the capabilities of this module are well surpassed by modern camera phone IC's the 30 fps x VGA rate could still be of substantial value in many applications. 

Omni Vision sensors product page - links to all sensor pages, including ...

VGA Sensors page

Also Application notes



These appear to be for related sensor ICs but may be of some use 

OV9740 sensor - 720p

OV10630 sensor - 720p

Data sheet for their 9655 camera



From OV7670 product brief.  

Based on a 3.6 μmpixel architecture, the OV7670
enables ultra-thin cameramodules of just 6 x 6 x 4.1mm.
This is a critical characteristic for slim camera phones
and notebook applications since the camera modules can
be no thicker than the LCD housing.
Also important in enabling such thin modules is that the
OV7670 allows module designs to move to a 2-plastic
lens design. Additionally, the OV7670's unique non-linear
micro lens shift technology allows for a reduction in the
distance between sensor and lens, shrinking the module
even further without loss of image quality or camera
performance.

The OV7670 employs OmniVision's proprietary
OmniPixel® architecture, which significantly increases
signal-to-noise ratio and delivers exceptional low-light
performance. Operating at a low voltage, the OV7670
image sensor provides the full functionality of a single
chip VGA camera and image processor in a small
footprint package. This includes full-frame, sub-sampled
or windowed 8-bit images in a wide range of formats
controlled through a serial camera control bus (SCCB)
interface.

The OV7670 can operate at 30 frames per second (fps)
in VGA with full user control over image quality,
formatting and output data transfer. As part of
OmniVision's next generation of image sensors, the
OV7670 delivers low-noise, low-cost, low-power
consumption, high integration, wide dynamic range and
excellent low-light performance.
Find outmore at www.ovt.com.