Hi Tunghsiao Liu,
I tried your new version, but there has not been a change. Here i put a little code so you can see in which part the url is not replaced. This img tag is created by calling the_post_thumbnail() function. every url in scrset is not modified by your plugin.
<img width="50" height="50" src="/wp-content/uploads/2010/07/2010-07-14-17822.web_-50x50.jpg" class="postThumb wp-post-image" alt="Strobist workshop with David Tejada" title="Strobist workshop with David Tejada" srcset="https://www.richard-vanek.eu/wp-content/uploads/2010/07/2010-07-14-17822.web_-150x150.jpg 150w, https://www.richard-vanek.eu/wp-content/uploads/2010/07/2010-07-14-17822.web_-100x100.jpg 100w, https://www.richard-vanek.eu/wp-content/uploads/2010/07/2010-07-14-17822.web_-50x50.jpg 50w, https://www.richard-vanek.eu/wp-content/uploads/2010/07/2010-07-14-17822.web_-120x120.jpg 120w" sizes="(max-width: 50px) 100vw, 50px" />
I have also noticed that url in feed are modified too (which is not good) so I have to add following lines at the start of the function which replace the url (done this in your 0.0.13 version.
if ( is_feed() || get_query_var( 'sitemap' ) )
return;