This plugin is outdated and might not be supported anymore
Post Script Responsive Images

Post Script Responsive Images

Details
View on WordPress

In short, this plugin modifies “the_content()” and the post thumbnail function by re-rendering the images with use of the SRCSET attribute. Other plugins do this for templated images, but not in the content region itself. This plugin will automatically work with any previously uploaded images as well.

Details

Plugin code:
post-script-responsive-images
Plugin version:
2.1.0
Outdated:
Yes
WP version:
4.0 or higher
PHP version:
or higher
Test up to WP version:
4.7.29
Total installations:
40
Last updated:
2017-01-06
Rating:
Times rated:
3
images
post-script
responsive
responsive-images
srcset