In the client file:
SpriteImage/eng-gb/common.spr
DDS file: common-8-23.dds is the premium image that appears on the loading screen when opening the game.
DDS file: common-8-26.dds is the premium image that appears in-game below the PvP point/Gold point banner.
When creating the new common.spr, replace the common in the following folders:
SpriteImage/en-gb
SpriteImage/en-id
SpriteImage/en-ph
SpriteImage/pt-br
SpriteImage/ru-ru