1. You need to read a book (or several) on image processing.
2. You need to learn how to design hardware, be it in Verilog or VHDL. There are some difference between these languages, the most important are:
- VHDL is strongly typed (like Pascal), Verilog is weakly typed (like C)
- In VHDL the explicit use of clock gaters for gated clocks is difficult, in Verilog its
easy. (Essentially, its equal easy in both languange, but clock gaters dont
simulate correctly in VHDL, while they do in Verilog.)
As you may need clock gaters (design for power is quite common now, and you need clock gaters for that), I would recommend you use Verilog.
Learning to design hardware will be the more difficult job. Apart from books, you should try to learn from how other people did it, by reading their code.