A huge amount of my images have a hard white edge in the editor and game. At first I assumed it was my images, but then I discovered if you shift the coordinates over by .5 on both coordinates it improves them the quality, some images it removes the line, others it just clears most of it up. Resizing or rotating can also cause the effect.
Have you tried to set “smooth the image” to “no” in the image bank?
Tried it before and it didn’t work, but it works now after I tried it again 
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