[racket] How do you convert an image made with 2htdp/image to a bitmap% object?

I wanted to have a button that was an image, and the button%  
documentation says that the label can be a bitmap, but the image that  
I want to use was created using the functions in 2htdp/image, and I  
don't know how to convert it to a bitmap.  I tried (send img get- 
bitmap), but it didn't work.  How do I convert an image made with  
2htdp/image to a bitmap?  Or else how do I make an image into a button?