1) the joomla editors usually convert the & character of the included URLs to & when this happens the plugin cannot work properly
2) your web server has to support Curl library (or allow_url_fopen which is not suggested because of security reasons), else the plugin cannot work at all.
I have made a little modification, so that the plugin creates thumbnails not for every resized image, but only for those who belong in a specific class. I describe those changes in case someone needs them:
In file mavikthumbnails.php, change line 156 from:
if ( $this->img->getHeight() || $this->img->getWidth() )
if ( ($this->img->getHeight() || $this->img->getWidth()) && $this->img->getClass() == 'mavik' )
In file imgtag.class.php, under the line 80 add the following:
$this->_class = @$this->_attributes['class'];
and at line 127 under the function getWidth() add this one:
Afterwards upload these two files to the folders plugins/content and plugins/content/mavikthumbnails respectively (replace the original ones).
From now on, to create a thumbnail for an image in an article, you have to define that the image belongs to class "mavik" (e.g. ) and use the mouse to resize the image in the editor. That's all.