Show Thumbnail: Flickr Feed

Show Thumbnail: Flickr Feed

I guess my question is simple to solve.
I want to show the photos of a specific album from my Flickr account. When I pull those photos, they come in medium format. I wish they came in the thumb format (75x75).
I made this code, but the pictures keep coming in medium format. What am I doing wrong?

<script type="text/javascript">
$.getJSON("http://api.flickr.com/services/feeds/photoset.gne?set=72157624413458897&nsid=45864612@N08&lang=pt-br&format=json&jsoncallback=?", function(data){
  $.each(data.items, function(i,item){
    $("<img/>").attr("src", item.media.m).appendTo("#personal")
      .wrap("<a href='" + item.link + "' target='_blank'></a>");
      item.media.m.replace('_m', '_s');
  });
  });
</script>

Thanks for the help.