I was scrolling through my posts and saw this one and figured i was sure i could do it now lol, anyways it turns out i can but its not the best, A limitation i will go ahead and address is that you may need to scale down the image because the outline will clip if its too large. (I will post a example)
(MODIFY FOR TRANSPARENCY)
Just for the record, i do not know what performance issues may come from sampling a texture parameter 9 times in a material, if that is an issue, you might be able to get away with sampling just the adjacent or diagonal samples. Here is another quick and dirty method that you can use if you are worried about sampling a texture that many times, i personally would not recommend because the result is subpar but i figured i would share anyway.
Images that are too large may cause the outline to clip (Because its relying purely on texture space)
