You can save the contents of the Display Window to a picture file. TkMedit uses the RGB format, a simple format readable by most image programs. To save a single picture, choose Tools->Save RGB.... You may want to turn off the cursor or other view items in the View menu before saving your picture.
You can also save a series of images with the Tools->Save RGB Series... command. This command steps through slices in the current orientation and saves an image of each. You choose a directory and prefix for the file names as well as the range of slices to step through. For example, if you choose /tmp for the directory, "image" for the prefix, and 5 and 8 for the start and end, it will create /tmp/image005.rgb, /tmp/image006.rgb, /tmp/image007.rgb, and /tmp/image008.rgb.