Anchun:
Thank you for your reply.
I'm sorry, but I'm kind of new to these. So you are saying, the Arduino processor is not fast enough, and those processors (Teensy..etc)
should be added to the Arduino board, to store images and do image processing?
So in that case, is Arduino acting just as a connecting board between the camera and Teensy (or other) processor?
and is the programming on Teensy still done through Arduino board and software?
I'm saying the Arduino is too slow and memory limited to do the job. It runs at 16Mhz, and only has 2K of read/write memory. You probably need at least a megabyte of memory, more likely much more to do anything.
In terms of embedded microprocessors, the Teensy, Due, Mbed are the next step from an Arduino, since they are built with a faster processor. However, as I said, it is likely that those processors while faster than an Arduino, are still not fast enough to do image processing in real time. For example, the Teensy 3.0 runs at 48Mhz (and probably runs faster than 3x of the Arduino due to instruction set, etc.) and has 16K of read/write memory. I don't know the other processors off the top of my head, but I would still think they cannot process images in real time.
Going to the next rung, which is microcomputer. These run at a much faster Mhz, and have much more memory, but generally they are not real time micro-controllers that are dedicated to a particular task. They usually run Linux or other more complex system. The Rasberry Pi, runs at 700 Mhz and has 256/512 megabytes of memory. You can pick up the model B R-pi for $35 and you will get either 256 or 512M of memory (old stock is 256M, they just recently updated the base configuration to 512M).
Besides something like a Raspberry PI, I suspect most of the modern Android phones have enough processing power to do it. I don't know what the details are for programming Android devices as compared to Arduino. Of course a normal PC that is of recent vintage is also probably powerful enough (the 486 sitting over in the corner with Windows 98 on it may not be powerful enough).