[ocius]

You can't really tell for a Web App whether it'll be faster in JS or Python, but you can definitely expect a Computer Vision application with lots of heavy number crunching to be a lot faster in C++ than in Python. We have actually also made comparisons, and even if you use things like numpy and Python bindings for OpenCV, you won't reach the speed that a C++ application achieves easily without optimization.

[catwell]

That depends a lot on what that CV application does and what hardware it runs on. Naive C++ (that runs on CPU) is usually much slower than using Python as glue for libraries that run on GPU.