Just for notice I link here a previous thread about a PDF printed with bad results.
If you follow the link to the “life in 19x19” forum, you’ll see pictures about how scaling can produce weird results on b/w images: look at board lines.
If you want to use pure b/w images, make them with the highest resolution.
Usually a colour image or a greyscale can be good enough for print with 300 dpi (dots per inch).
Pure b/w (sometimes called “bitmaps”, don’t know why) need at least 600 dpi.
Luckily, because of the reduced colour depht (just 1 colour), b/w images can produce smaller files even with a huge resolution. Expecially if they have big clear zones of white and black (no dithering or textures) as it should occour with clean goban diagrams.
Otherwise a vector format would be better, but I don’t know how you could produce vector diagrams.
You could draw them with a vector editor (such as Corel Draw or Adobe Illustrator). But it could be hard work because they for sure don’t know what a SGF is.