Weathering steam engines and locomotives is something i’m going to try very soon. So finding good prototype images to see how steam engines look after heavy use is my first step. Though quite fast I realized that it was going to be hard to find good reference pictures when all the period images are in black & white. Therefore I found some more recent pictures of Chinese locomotives in full color to be more accurate for my weathering ambitions. Yes they still use steam locomotives to some extent today. Check it out:
Youtube also offers a lot of references.