This plugins allows you to requests for inline images on html messages on roundcube through a imageproxy instance. It is useful for forcing such requests to be made on https, to modify images on the run.
I am specially using it in conjunction to a serviceworker plugin (soon to be released) to allow access to linked images on a pure https instance. To avoid misuse, this plugins only works with a imageproxy instance configured to use Signed Requests.
I run a local imageproxy instance on localhost, configured to cache on a local redis instance, something like this:
imageproxy -addr localhost:8080 --cache redis://localhost/ -verbose -signatureKey VeryLongSignaturestring
On the roundcube hosting vhost,
ProxyPass /imageproxy http://localhost:8080
ProxyPassReverse /imageproxy http://localhost:8080
On the plugin configuration,
$config['imageproxy_url'] = 'https://webmail.example.com/imageproxy';
$config['imageproxy_signature'] = 'VeryLongSignaturestring';