300dpi at whatever physical size you want. Printing at 1 inch x 1 inch? 300px x 300px.
It also would be really cool if one could ”carve” the lines to the paper. Might be possible with a plotter and the right kind of stylus.
A while a go I bought an artwork that actually was cut out from an issue of Harpers’ Magazine c:a 1860 or so. One thing that’s really cool about that line art is that the printing technique made the lines embossed to the paper. Beautiful!
If you're looking for a way to turn a bitmap into a vector type thing, for a plotter or laser or so on, then potrace or the bitmap->vector converter inside Inkscape should be able to do it. They work well for line art.