img[src$='#center'] {
  display: block;
  margin: 0.7rem auto; /* you can replace the vertical '0.7rem' by
                            whatever floats your boat, but keep the
                            horizontal 'auto' for this to work */
  /* whatever else styles you fancy here */
}

img[src$='#floatleft'] {
  float: left;
  margin: 0.7rem; /* this margin is totally up to you */
  /* whatever else styles you fancy here */
}

img[src$='#floatright'] {
  float: right;
  margin: 0.7rem; /* this margin is totally up to you */
  /* whatever else styles you fancy here */
}