Some posting above have said they don't see the potential for large numbers of contributors. I would suggest to you that maybe that's not such a bad thing. In the early stages this would enable the moderators to review the contributions more carefully and to eliminate repeat loading of the same materials (which will certainly happen). I would also suggest to you that as the ball starts rolling and more and more material is loaded, possibly more contributors would be attracted.
I would happily contribute to such a reference. According to the properties menu on my computer, I have 7.90 Gb in 20,766 files separated into 1,299 folders of mostly World War 1 material. There are at least a few useful images and text related to the conflicts from 1870 to about 1951. The images include uniforms, field equipment and weapons. I've been collecting this stuff for 12 years and continue to add to it. Some comes from web sites, some from magazines, books, etc., some from friends who know I have an interest in collecting images of this period.
For copyright control and other reasons, I would have to be edit extensively and carefully cull images and text before sending it to Planetfigure. Unless the artist or their estate gave prior approval, personally I would not load illustrations and paintings out of concern for artist copyright control. Photos from magazines still being published and reference books - again speaking only for myself, I would be very careful what I sent to Planetfigure.
All the best,
Dan