With thanks to 04nbod who was the one that made me aware of this in the first place: there is hidden secrets on the BBC Who site!
If, while on the Doctor Who homepage, you change your computer clock to a date after Silence the Library will air (or even just a few days before), then the book thats part of the picture will flips a few pages forward and briefly reveals this:
It is Rose!
It doesn't stay on this image as the book flips to a page saying "5 Days to go" or something similar. The Rose image can only be seen very briefly. However, If you alter that day on your PC clock, whilst looking at the homepage for 'Silence In The Library', you can see the image of Rose as the page flips.
Apparently there is rumour whether it is true or not, that Donna will burn the Doctor's book and the last page having a picture of Rose on it? Or will we just see a glimpse of Rose in a random book?