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Open Paint with that picture and use the Bucket Tool pour the Color outside of the Image try using a dark color you should see lil white dot outside the black outline of the picture that you should get rid of. Also make sure that the Tranparent color does not match any of the color that the picture is using.
if that don't work upload image please and I'll personally check it.
As you can see where the white dots are when I pour green in the back. The only thing you can do is edit it yourself and get rid of the white or fill it with Near Black(Not Pure 0,0,0 Black).
The lines/dots are a result of anti-aliasing, which is a problem for transparent images. Unfortunately the only way to fix it is zooming up and manually deleting the extra lines/dots.