You can use OSGeo4W to install the OTB Libs. Run the setup again and choose Advanced Install then go through the options until you can select the packages. Type in otb in the search tab:
Then click each package as shown in the red box (I installed it before taking snapshots). Finish the installation then load QGIS and go to the Processing Provider options ...
There are four steps to perform an object-based classification in OTB:
1) Image segmentation
note that there is also an external module with the Baatz and Schape criterion : http://tully.ups-tlse.fr/lassallep/grm/tree/master
2) Feature extraction in order to compute object-based variables for the classification
OTB python bindings are prebuilt for a specific version of python3 which I think is bit older than python3.x used in OSGeo4W
Possible workarounds: (order of increasing difficulty)
Check if OSGeo4W can use same python version OTB uses in its built. If so, reinstall qgis with that python version.
Install python version used by OTB and call "import ...
From release 5.4 OTB will distribute standalone binary packages which contain all exe and applications in a self contained archive for LINUX/Windows/Mac.
5.4 is not released yet (targeted for May) but you can already try it (nightly package are available on a daily basis).
32 bits system:
Unless I am misunderstanding your needs, I can recommend the use of Semi Automatic Classification plugin in QGIS, which is actively developed and very well documented, and in which a complete dataset composed of any amount of bands of any number of files works as input for the classification.
I have always found it simpler to calculate indices over my whole image, then mask the result with whatever mask I need.
The only problem with this method is when the "unmasked" area is very small and distributed all over the image....but even then, if you just want to calculate some simple indices, you may not need bother with extracting those specific ...
If you rely on Orfeo toolbox, I advice you to use QGIS 2.14.20 LTR (Long Term Release) the split tool is still there. I am not sure why the Split Image tool is removed from QGIS 2.18.14 but I can confirm that QGIS 2.14.20 still has the Split image tool:
QGIS 2.14.20 (Split image tool exists):
QGIS 2.18.14 (Split image tool does not exist):
I had the same problem and I think it is due to the space between "Program" and "Files" in "Program Files". Try moving the OTB binary package to your C drive and repeat the process (Making sure there are no spacews in your file folder path). Then restart QGIS. This worked for me.