Raw camera modules like OV7670 just spit out a stream of data at a high speed, and it is up to the user program to capture it at the right HSYNC and VSYNC points in time. It is uncompressed, raw data. Also a fair amount of memory is needed, i.e. number of pixels in X direction times Y direction, so about 300kbytes for a 640x480 frame with 8 bits per pixel, which is only 256 colors, so in practice you want 16 or 24 bits per pixel.
However, the instructables page shows some camera module with RX and TX pins only. So it seems to be some module with on-board processor which captures the stream of data into memory on the module, and makes it available over a UART, perhaps compressed (e.g. JPEG frames like a camera, so less memory is needed). But OV7670 is a part number for a raw camera module, so they have forgotten to mention the actual module.
Their module should be fine if your requirement is to capture individual frames, but without knowing which module they mean, it is not possible to tell if it is suitable.
If you have access to an Intel Galileo then there is a whole chapter on using USB web cameras with OpenCV in Manoel Carlos Ramon's book "Intel Galileo and Intel Galileo Gen 2: API Features and Arduino Projects for Linux Programmers"
( It's an 'open access' book so you can take a read here:
It covers image and video capture along with image processing such as edge detection, face and eyes detection and so on. You may be able to apply these techniques on the pcDuino platform as well.
