I'm looking to create a "retro" effect on some images. I don't know a better name for this style, the main features of it being few colors, flat design, and bold outlines.
My inspiration is the posters of US national parks made in the 1930s that have a retro/vintage style to them that I'd like to recreate on my own images. What are some tools that I could use to achieve something close to this? Ideally something in script form that I could apply to a big set of images.