ARM Processor or FPGA to video signal processing?
The reason Dave asked you what you want to do is because what path you pick will depend on your goal.


What will the interface be to your camera?  HDMI, Composite, YUV,
directly to an image sensor etc? 
What frame rate and resolution do you want to work with?
Do you want to process every frame?
What are you going to do with the video data something simple?  Something complex?
Is this just a school project, work project, proof of concept?  Can you afford a suitable FPGA in your final cost?  How about a suitable FPGA development board?
What's your skill level in FPGA design vs embedded software?


You can do a design any number of ways but you have to consider all of the tradeoffs before you make a decision.  There are small fpgas, large expensive ones, generic ARM processors, video processing specific processors (some that you'll only get if you are a large volume customer).

Based only on the limited information you supplied I would say if your budget and ammount of processing per frame rate are low take a look at some arm processors.  You might even consider a lower cost FPGA like a lattice, or low end spartan or MAX.

If your frame rate and processing needs are high, and final cost is not an issue take a look at a higher end FPGA as a solution.

If your frame rate and processing needs are high, and final cost is an issue, design an ASIC :)