I recently posted a link to a wonderful website which offers HiRes pictures of posing nudes on my Facebook channel.
Check this website out: http://www.posespace.com
And also this one: http://www.female-anatomy-for-artist.com/site/index
With the pose tool (http://www.posespace.com/posetool/Default.aspx) you can see all of their model’s poses. As a non-member these are low-res photos and as a paying member you have access to hundreds of hi-res photo references.
Registering is free (with two hi-res samples as a “welcome gift”).
Also take a look at the artworks that have been created with these references: http://www.posespace.com/artists/default.aspx
Without registering you can also access one free HiRes sample, which I did yesterday evening. Then I took some cheap drawing paper pasted on the backside of a wood panel, pencils grade F and 4B and a kneaded eraser. After 4 hours of work it turned out quite well.
I did not zoom in; I just left it the height of my screen.