Image processing hardware options
If you have a bit of budget, the Xilinx Spartan 6 FPGA is quite well suited to video processing. You can even buy a complete kit for about $5K. The link has some reference designs which you can compare to what you are trying to accomplish. 

Since you don't know exactly what amount of processing is required, it might be better to err on the side of more capability than you think you'll need, so you don't run out of room on a given approach. You can always downsize to a smaller FPGA.