In which case, can I ask why this would be helpful? Maybe we can have a little discussion and get around even needing the dll in the first place, and keeping your game portable across every platform love supports.
I'm using the GD library that came with my Lua distribution, which I believe is what you say, yes. I am using it so I can combine and manipulate multiple images together and then save them as a temporary tileset for a SpriteBatch. I am assuming it's probably is a poor tool for my job. I was looking just for a library to manipluate image files directly.
I don't know if this would replace what you're using gd for, but Love's image library has some features for merging multiple images together: https://love2d.org/wiki/ImageData
In one older project I have, I take a single image that my artist made with weird dimensions, load it into an ImageData, and then paste from it into another imageData that fits the PowerOfTwo requirement for textures. If that's enough for you, and you don't do any other special things to the image, then you can ditch the gd requirement altogether and not have to worry about including .dll's or .so's for every platform you want to support.
Side Note: the ImageData:mapPixel function might be neat to play with if you do any special manipulation of images.