You can apply custom key images to mania key columns, via the mania.ini files.
To use this feature, if you set KeyImage0 value to (String 1), it uses (String 1).png image.
Also the KeyImage0D value of (String 2) uses the image (String 2).png.
To use this feature, if you set KeyImage0 value to (String 1), it uses (String 1).png image.
Also the KeyImage0D value of (String 2) uses the image (String 2).png.