Drag n drop on iframe

Hi,

I am developing an application where user can drag an image from group of images and drop it on one web page.
I am opening this web page in iframe. My problem is that i need information about the underlaying HTMl element details where image is droped. HTML element can be anything, it can be "DIV, textbox, table and so on .....".

Please give me any idea of how to achive this ......