You can take image as 2D array, then you can find some 2D FFT c sample codes in MKL install folder or web article.
MKL support several model like sequential, internal openmp threads and tbb threads, which are suppose be work with external pthread.
If you have any question, please submit your question to https://supporttickets.intel.com.
MKL support N-dimensional FFT computing, you could follow developer reference or MKL examples saved locally when you install the MKL, the path is $MKLROOT/examples.
MKL threading is using OpenMP/TBB, but you could write pthread program to control outside.