How do I install OpenCV 3 on Centos 6.8?

Question

I'm working on a CentOS cluster right now and have Python2.7 installed. I've managed to get OpenCV 2.4 installed (using these helpful instructions) but it does not have all of the functionality of 3 (I need the connectedComponents function and a couple others not available). Omitting the "checkout tags" step results in errors during "cmake". Something else to note is when I attempt to install the ffmpeg package it tells me no such package is available. Error:

CMake Error at 3rdparty/ippicv/downloader.cmake:77 (message):
  ICV: Failed to download ICV package: ippicv_linux_20151201.tgz.
  Status=6;"Couldn't resolve host name"
Call Stack (most recent call first):
  3rdparty/ippicv/downloader.cmake:110 (_icv_downloader)
  cmake/OpenCVFindIPP.cmake:237 (include)
...

Answer 1

I've managed to get OpenCV 2.4 installed (using these helpful instructions) but it does not have all of the functionality of 3 (I need the connectedComponents function and a couple others not available).

Why don't you just download OpenCV 3 then?

Something else to note is when I attempt to install the ffmpeg package it tells me no such package is available.

You can download the file yourself from here (the package that is not available for you).

Then place it in the folder where it initially would have been downloaded to:

<your opencv build>/3rdparty/ippicv/

Answer 2

It seems like OpenCV 3 would be better suited for what you are doing, you even said yourself that you are needing features that aren't available in 2.7.

The OpenCV 3.0 documentation actually has a full guide on installing the latest version of the library using the Yum feature in your terminal. It walks you through every step and explains them all in detail, including the Cmake steps which seem to be giving you trouble. I would recommend taking a look at the guide which is linked here.