I have found a Russian website that seems to get Doctor Who images before episodes are broadcast. For example, this is from Episode 7, due to be shown on 4th June.
(Click image for site)
If you aren't able to translate the caption under the image, it says "THIS IMAGE IS UNDER STRICT EMBARGO UNTIL 00:01HRS 12TH APRIL 2011", so it seems that the BBC have 'released' this image to publicise the upcoming episode, but I'll be keeping an eye on this site, watching for more spoilers...