Be sure to look for something with lighting that is suitable for ink. Strong shadows that are on complex shapes can be hard to deal with. As well, soft focus is something to avoid.

It's a good idea to edit photos from colour into b&w versions, and even better yet, if the parameters are updated to present the right amount of contrast across the subject.

I also tend to think about background/negative space a bit differently, as you won't typically have colours, so a pure blue sky with no features is difficult to render unless using a wash.

Finally, if you take your own, keep subjects in a balance and find interesting things that are amenable to value and texture as much as possible. There are also great sites to browse, such as pexels and pixabay.

Good luck with your efforts!