hi

You can use imagej  , stack with fft plugins e.g.

http://rsb.info.nih.gov/ij/plugins/fftj2.html

Cheers

 @ Narasim Ramesh : Thank you very much for your response. 

@Dinesh K. Vishwakarma: Thank you very much for the codes. Frankly speaking, i didn't understand the codes. Can you please send me the codes again considering that i have 20 different images and would like to know the magnitude and phase of those images.

Hoping to hear you soon.

@shreshta the above code give by @vishwakarma define for the one block of an image. For your concept, I think we can go with the concept of arrays. Storing each image in an array and apply similarly the block code to calculate the magnitude the phase spectra. This thing go with the sequence of 20 images