I have changed the code in flickrrss.php begining in the line 266 to
this:
# builds html from array
foreach ( $items as $item ) {
if(!preg_match('/src=["]?(http:\/\/.*\/.*)_m\.jpg["]?/', $item
['description'], $imgUrlMatches)) {
continue;
}
//$baseurl = str_replace("_m.jpg", "", $imgUrlMatches[1]);
$baseurl = $imgUrlMatches[1];
$thumbnails = array(
'small' => $baseurl . "_m.jpg",
'square' => $baseurl . "_s.jpg",
'thumbnail' => $baseurl . "_t.jpg",
'medium' => $baseurl . ".jpg",
'large' => $baseurl . "_b.jpg"
);
And this solved the problem at least for me.