Understanding Magnitude Spectrum of Images
Many people face the same issues. Your image is far from showing stationarity: quite edgy, with circular features, so the Fourier analysis might not be so enlightening, without showing the unwrapped phase, which might contain many interesting features for this class of images. However:


so there is a dot in the middle: standard images have integer values between $0$ and $255$, hence the average is not zero. The average is the center dot. Remove it, and the global contrast may be better
some striking vertical and horizontal lines: FFT generally uses periodic extension, and the differences between the bottom and top, and right and left, might obfuscate details.


In the following pictures, you get space data and the Fourier spectrum. The first line is your image, with an horizontal/vertical cross. When you window the image (second line), those disappear, and the most luminous  decreasing slope is, probably, due to the index finger, and the parallel lines from the two biggest gears. On the third row, the windowed image is subtracted from its  median filtered version.  One begins to see circles, related to locally oriented teeth.



So, to interpret complicated data, remove first order artifacts, and slow background features, to better interpret details.