Image Processing with Java

I'm writing an image processing program that needs to be multiplatform, so I've chosen Java. I've been trying to use OpenCV via JavaCV, but I'm finding that all of the documentation for OpenCV is only in languages I don't know, and there is only a small amount of incomplete documentation for JavaCV.

All I need to do is check black only and white only webcam feed every few milliseconds and count how many white boxes are visible, then log the data, which I've already taken care of

Any recomendations for something other than JavaCV that has documentation I can use or another method of solving this?

Use C++.  If you don't know C++ you should learn it.  It's very similar to Java, with the benefit of being somewhat faster.  It's not compile-once, but in practice it's as cross-platform as Java is; OpenCV itself is written in both C and C++ and it is cross platform.