# Palmprint Identification - Why do we align the images before we use the Fourier Transform?

I was reading the paper PALMPRINT IDENTIFICATION BY FOURIER TRANSFORM by WENXIN LI, DAVID ZHANG and ZHUOQUN XU about identifying persons based on an image of their palm.

• The first step in their identification algorithm consists of aligning and pre-processing the image since they spent a few pages on that front, this gave me the impression, that this step is kinda important.

• What I didn't understand however: Why do we do this? The essential part in my opinion is the Fourier Transform afterwards, that is used to extract/generate the feature. But from my understanding, this should even work without this aligning/pre-processing step.

• In order to extract features, some rotation might be necessary, at some point. In my opinion however, this does not justify to think up such an elaborate method of aligning/preprocessing the image, there has to be more behind that.

• Therefore, I am most likely overlooking/missing something. Thanks in advance.

• @OlliNiemitalo second link Mar 28 '20 at 7:25