How to use readClipboard to read a bitmap when using R?

I don't managed to read a bitmap which is in the Windows clipbard. I first check the cliboard :

getClipboardFormats()

which give

[1] "bitmap" "DIB" "shell"

Then I tried :

image = readClipboard(format=2, raw=FALSE)`

and

image = readClipboard(format=2, raw=TRUE)

but I always obtain a NULL value for image ! Can someone explain to me how to do it?