When you crop a photo, you are essentially removing a portion of the original image. This means that you are reducing the total number of pixels in the image, which can lead to a loss of quality. The amount of quality loss will depend on the size of the crop and the resolution of the original image. In general, the larger the crop or the lower the resolution of the original image, the more noticeable the quality loss will be.
Additionally, if you are cropping an image to a significantly different aspect ratio than the original, you may need to stretch or compress the remaining pixels to fit the new dimensions, which can also result in a loss of quality.
It is generally a good idea to crop an image as little as possible and to try to maintain the original aspect ratio whenever possible to minimize the impact on image quality.