If you want to learn more about image processing with FPGA's I recommend this book
https://www.amazon.com/Design-Embedded-Image-Processing-FPGAs-ebook/dp/B005FXVEDY
As for which board to buy, I'd buy something that is a Xilinx Zynq, so it's easier to get camera data into the FPGA fabric, process, and then look at the results.
I can recommend this book: https://www.amazon.com/Design-Embedded-Image-Processing-FPGAs-ebook/dp/B005FXVEDY