That's pretty cool! It would be nice if the API allowed writing to io.Writer instead of taking filenames.
https://godoc.org/github.com/mmcloughlin/globe#Globe.Image
This can be passed to an image encoder like
https://golang.org/pkg/image/png/#Encode https://golang.org/pkg/image/gif/#Encode https://golang.org/pkg/image/jpeg/#Encode
These functions take io.Writer objects. SavePNG was provided for convenience.