You have not specified a budget or a technology preference (OpenCL vs CUDA), so I will attempt to run the gamut, with one important inclusion that you did not mention but which I see as fairly important for your purposes: USB C/Thunderbolt 3.
If you're running a budget and you need something that's going to make the most of a program stack utilizing OpenCL, I recommend something like the Acer Laptop Aspire E5-553G-1986. This AMD Crossfire machine features the company's most powerful processor currently shipped in the mobile market, coupled with (at LAST) high-speed DDR4 RAM in a dual channel configuration, upgradable to 16gb. It features the dedicated AMD Radeon R8 M445DX GPU combined with the powerful graphics chip on the APU itself, which should provide quite a bit of AMD's noted OpenCL GP-GPU capability.
On the other side of things, in the high-end range, Intel and Nvidia dominate in professional solutions such as the Dell Precision 15 5000 M5510. Intel's full-power mobile i7 CPU couples with Nvidia's professional Quadro M1000M GPU to deliver what is no doubt one of the more powerful and reliable solutions available on the market. If your program is CUDA-bound, then this is more like the machine you want. If CPU processing power is the main drag, then this too will be your best bet; Intel's i7-6700QM is pretty much unrivaled in the mobile space. This machine is also extremely light - unusual for Dell's robust professional line.
I'd like to end by touching on the inclusion of Thunderbolt 3/USB C in both of these laptops. Whatever you do, the time may come when you just don't have enough GP-GPU compute resources available to you - or perhaps you end up needing a solution from the company that doesn't feature a GPU in your laptop. In those cases, you can use this new connection type to add external GPUs to your laptop in order to greatly improve your image processing capability.