Rich Text box Problem

[abhi]

I have a Rich Text Box Control. In which i want that only text along with its formatting(bold, color etc) be pasted. But it should discard IF clipboard item contains Image.
I tried using
if(!(Clipboard.GetDataObject().GetDataPresent(DataFormats.Bitmap)))
{
Clipboard.GetDataObject().GetFormats();
this.Paste();
}

but does not allow Image to be pasted but if data to be pasted contains Image and Text both it fails to restrict.
I also tried with DataFormats.Text but then only text is pasted and formatting is lost. Can anybody help me.