There is only one file type that uses the .OZT extension:
MU Online Image File
Image file created for MU Online, a massive online multiplayer role-playing game; contains a graphic referenced in gameplay, which is used for character appearances, textures, interfaces, etc..
The OZT file must be converted into a .JPG, .BMP, .TGA or other editable image file in order to be modified by an image editor then converted back into an OZT file. The OZT file can be converted using the MU Online Image Converter.
NOTE: Other similar image files used by MU Online are .OZJ and .OZB.
Updated: September 26, 2013