adding a custom button to open a popup

For a website I am building I am using CKeditor. Before starting to use that, I already created a page to upload a image, that works all very well, it automatically resizes images, gives them a unique name, regsiter them in a database and than present a code like [img]123[/img] to the user. The user can later use that code in a description, and when rendered, the code gets replaced by the view script with the proper html IMG code.

Because I've got all that working and in place already, I do not want to use the CKeditor's image browser.

The difficulty I now have is that users have to upload a image, and remember (or copy/paste) the code they get. Instead of that, I would like to add a button to the CKeditor windows that pops up the already working upload form, and after the upload is completed, it should insert the generated code into the tinymce editor. (the code like [img]123[/img] )

Any idea if this is possible?