Enables shortcode and a template tag to pull srcset-images by attachment-ID. This is way to complement WordPress built in srcset which (of course) focus on the_content images and media-sizes set in settings. Sometimes your layout demands more, or you are using other ways to put images on your site not using the_thumbnail or the_content. For example, I use Advanced Custom Fields a lot pulling images by ID.

Generated markup are built from a set of custom image-sizes and the, by you configured, (srcset-)sizes attribute. Use the settings-page for default values and override them any time in the shortcode or template tag.

Option: Generate shortcodes by the mediauploader-button.
Option: Enable simple lightbox functionality.
Option: Enable lazhyloading. Option: Include Picturefill

Full documentation at WordPress plugin: Make it Srcset