The problem is that you cannot run that “import-bmp” when making a library part, but there is a easy workaround.
Make the image
Take any image you like. For instance, when using photoshop, take any image: then firstly go to the histogram: then tune the histogram curves so you get a black-white image. Then convert to bitonal image, then save as bitmap. This image really has to have a resolution of ~300dpi.
Getting the image to Eagle
Make a new project, open a board file, run the import-bmp with some values (you figure it out). Now, select this entire image and COPY it.
Getting it into the library
Go to your library, go to “make a package” and just go in there and “PASTE” it. It’s as easy as that. Make a device from it and you’re essentially done for further use!