Cgi::application::plugin::ajaxupload provides a customisable run mode that handles a file upload and responds with a json message like the following:

{status: 'uploaded', image_url: '/img/uploads/666.png'}
or on failure

{status: 'the image was too big.'}
this is specifically intended to provide a cgi::application based back end for allmybrain.com's image upload extension to the yui rich text editor. it could probbably be used as a back end for any cgi::application website that uploads files behind the scenes using ajax. in any case this module does not provide any of that client side code and you must also map the run mode onto the url used by client-side code. that said a working example is provided which could form the basis of a rich text editor.