I am new to ImageJ and have been going through some of the materials provided to gain a better understanding of the software. I currently have a large set of radiographs of which I am only concerned with a small rectangular window, so I would like to find a way to crop the images down to the size of the window for further processing. This window, however, is not entirely static throughout the set of images. I have messed around with thresholding the image, however there are similar values outside the window as well as inside, so this is not entirely helpful. Can anyone provide me with some advice for moving forwards? I have attached an example of the radiographs.