So are probably not able to do this using openCV on a PIC. It looks like openCV is more meant for userspace applications on Windows, Linux, etc. Extensive porting may be required and is probably not what you are looking for to start with a PIC. Also it would matter if it was a PIC10, 12, 16, 18, 24, 32. The word size varies between them: 8, 16, 32 bits. The PIC32 is actually MIPS versus Microchips hardvard PIC architecture. The cores also vary in terms of implementation for example hardware multiply. This would all come into play in determining performance and what would be required to port it. Also the program memory alone would probably be a deal breaker here.
openCV may be possible on something like a Raspberry PI or Beagle Bone.
You probably could do image processing on a PIC, but this would be for more of an exercise of theory than practicality. The question is how fast, how complex of image processes, and how large of an image. I would recommend starting out with custom code, as you will probably be doing that in the porting process alone. (You could take concepts from it though.) So it could do simple things like flipping the colors and stuff. However for much more I would recommend a larger processor. A PIC32 and maybe a PIC24E/H would be a good place to start.
Just to be annoying: So RAM could be worked around using external memory, but that would be really slow. Again the lack of an ALU does not make it impossible, just slow. Now not having an ALU will increase the program size which most microcontrollers do not allow external program memory. (Now you could make program the reads an external memory chip that executes the instructions from that. Which would be really really slow and inefficient.) For example someone claims to have built a ARM emulator on a PIC. Then proceeded to use this to boot an ARM distro of the linux kernel. It took forever, but supposedly worked.
What kind of camera it was would determine how to connect it. Again there are lots of little tricks to make it work, but you would probably not want to do any of them in practice.