Palmprint Identification - Why do we align the images before we use the Fourier Transform?
From the article:


  [...]only a sub area of a palmprint image is used in feature extraction.


The alignment by a shift and other image transformations is done in the full hand image which is then cropped to a sub image containing only the features of interest. To analyze the sub image they Fourier transform it. They are not shifting the sub image alone but the full image so the shift operation does not have a direct equivalent operation in the frequency domain of just the sub image.