I don't think GW cares about using the pictures of the box cover and book covers as long as your not selling anything. But that does mean ANYTHING, if a site is using the pics and has say collects money from advertisers on their website then thats a no as well.
I've seen other forums do roughly the same thing you guys are planning. Box pics, sprue pics, etc...
Heck, the websites started doing the sprue pics and then all of a sudden GW decided to post pictures of their sprues on their website - I guess they do look at what the community is doing. They have sprue pics for 40k, not fantasy though.