Get a 128x128 pixels of image and cropped it into a circle. Then, save the file with "hitcircleoverlay.png". Remove the hitcircles by adding a blank image and named it as "hitcircle.png".
Or you can also save the image with "hitcircle.png", but it will be tinted with colours. Therefore, I suggest you to use "hitcircleoverlay.png" if you don't want any of your images got coloured.