I usually just link to it from the template using the image function, and let Typst do all the hard work. It took me a while to fiddle around with paths but if you want a quick hack the priv directory is easily accessible and you can write to it. I wouldn’t do that on public facing apps, using phoenix for example, unless I’ve rigorously configured the static routes not to include those “temp” directories.
Another solution would be to use the image.decode “function” as the last example here
In one instance I found it easy to use packages from the Typst Universe (their package directory) I had used this one “tiaoma – Typst Universe” when working on a logistics project. These ones are rather hard to integrate with ex_typst out of the box as you would need to modify the world struct from the rust side or include the dependency while compiling with rustler.
Sorry for the long rant, I hope this was helpful.
EDIT: When using json. I include the path to the image in the data.
