If you have some code outside of CKEditor that inserts an image into its content and then you want to automatically launch the ImageMaps dialog on that image, you can use simply this two lines of code:
First, select the image using the CKEditor API:
"editor" is a reference to the editor instance that contains the image, and "myImageID" is the id attribute assigned to that image.
It first gets a reference to the element with editor.document.getById and then tells the selection system to select that element.
Then launch the dialog: