The Retronaut website has a great series of images of tanks from World War One in one of their recent blog posts.
If you are thinking about making some scenery for games in this period, these photographs really do give you some interesting ideas.
There are a fair few images of damaged or immobilised tanks and so again useful guidance when making abandoned tanks as scenic pieces.
If you want to see a fantastic looking demonstration game from World War One, then here are some photographs from Aly Morrison’s excellent game at GamesDay 2007.