I have tried to build OpenCV 3.2 with libjpeg-turbo 1.3.0. It crashes in imwrite without any error message. Then I fallback to the libjpeg version used by Qt 5.8. That works.

The build Instruction

1) Download opencv 3.2 and opencv contrib 3.2 and extract them:

$ ls opencv-3.2.0 opencv_contrib-3.2.0

2) Download libjpeg source code

Since I have already downloaded the Qt 5.8 source code, I simply use Qt's version.

3) Patch opencv-3.2.0/platforms/ios/build_framework.py

--- build_framework.py.orig 2017-02-13 11:12:14.000000000 +0800
+++ build_framework.py  2017-02-13 11:13:42.000000000 +0800
@@ -135,6 +135,7 @@
             cmakecmd.append("-DENABLE_NEON=ON")
         cmakecmd.append(self.opencv)
         cmakecmd.extend(cmakeargs)
+        cmakecmd.extend(["-DWITH_JPEG=ON", "-DBUILD_JPEG=OFF","-DJPEG_INCLUDE_DIR=/opt/libjpeg-turbo/include", "-DJPEG_LIBRARY=/opt/libjpeg-turbo/lib64/libjpeg.a"])
         execute(cmakecmd, cwd = builddir)
         # Clean and build
         clean_dir = os.path.join(builddir, "install")

You should change the parameter of -DJPEG_INCLUDE_DIR and -DJPEG_LIBRARY according to your environment

-DJPEG_INCLUDE_DIR = Path to the source code

e.g ~/qt-everywhere-opensource-src-5.8.0/qtbase/src/3rdparty/libjpeg

-DJPEG_LIBRARY = Path to the libqjpeg.a from Qt SDK

e.g ~/Qt/5.8/ios/plugins/imageformats/libqjpeg.a

4) Build

cd opencv-3.2.0
mkdir build
cd build
../platforms/ios/build_framework.py ios --contrib=../../opencv_contrib-3.2.0