I've quickly browsed the pages of this thread and maybe I've lost some useful link, so I need a simple schematic (I would like to try with resistors to pull-up the pins and to match the 3,3 V level inputs of OV7670) to connect the camera to arduino.
Firstly, you have to figuring out if your version is the fifo or the non-fifo one, otherwise the schematic might change.
The non-fifo version have 18 pins :
D0..D7 - for data (pixel) connected to arduino digital pins as INPUT on arduino board
XCLK - for camera clock connected to arduino digital pin as OUTPUT from arduino board : you have to generate a clock
(I am lost on this part : the documentation that I have found on oscillators/PWN/timers/interruptions is non-specific to the arduino MEGA2560 and haven't been able to replicate it....)
PCLK - for pixel clock connected to arduino digital pin as INPUT on arduino board
HREF - to define when a line starts / ends connected to arduino digital pin as INPUT on arduino board
VSYCH - to define when a frame starts / ends connected to arduino digital pin as INPUT on arduino board
GRD - groud connected to arduino GRD
3V3 - 3,3 INPUT connected to arduino 3,3v
RESET - connected to arduino RESET
PWDN - connected to arduino GRD
SIOC - to communicate on the SCCB/i2c : the user, through the arduino, as to drive it in order to assert the data that are being written/read through SIOD : you have to connect it to a digital pin if you use a bitbanged implementation of SCCB/i2c or to the SCL pin of the MEGA2560 if you use the hardware i2c ; unless I am mistaken... Anyway, it's an OUTPUT.
SIOD - to communicate on the SCCB/i2c : alternativaly, the user may drive in order to write (OUTPUT), or it's the OV7670 which drives it whenever there is a data that is being read.
If you happen to have the fifo version, you'll find a schematic here :http://nicolasfley.fast-page.org/?page_id=35
The code I've seen on github is C or C++ (objective C) : can I copy that code and paste into the editor of arduino IDE?
The code you have seen is written in C, mostly, and you cannot copy/paste it directly into the arduino IDE editor.
You may want to consider this :http://www.vascop.com/compiling-and-uploading-arduino-programs-without-the-ide.html
Nevertheless, you may copy/paste some parts directly into the arduino IDE editor but be careful since the code you may have seen deals with registers directly and it can be very tricky sometimes if you do not know what you're doing...