Common reasons:
In the architecture of PES 2013, game data is stored in compressed, container-like files with the .img extension (image file format, though they hold far more than pictures). These files live in the img folder of the game’s root directory. The naming convention follows a logical structure:
Put simply, if you see a pitch, a stand, a tunnel, or a floodlight reflecting off the turf in PES 2013, that data is almost certainly being pulled from dt03.img.
You might ask, "If Kitserver allows external stadiums, why edit dt03.img?"
The answer is Stability and Base Texture Replacement.