Not compatible with caching plugin (W3TC)

Plugin doesn’t work with caching plugin, in my case W3TC. Problem is with page caching: it caches page HTML so as GET parameters of securimage_show.php that are in img element src attribute, therefore page shows one captcha image while during submission it is expected different input value.

This could be solved having fixed URL in captcha’s src attribute of img element. Not sure how complicated that would be to implement on this plugin. When I had my own captcha plugin for different system I was storing parameters in session and was calling PHP script without GET parameters, however, I haven’t adopted that solution to WordPress.