The replacement PNG files can have larger dimensions when compared to
the original XMG images, enabling the creation of a high resolution mod.
The game looks for the replacement files in the game directory and then
in the xarc subdirectory of the directory containing the archive in
which the xmg picture to be replaced is located. For instance:
'1e/00/xarc/fountain_layercenter.png' should be used for the Venice park
background.
