Archive files in Grand Theft Auto games since GTA3 have used the .img extension. They generally contain all of the DFF models for all solid objects in the games, as well as TXD files which hold all of the textures for the said models.
If you want to add your own, or replace models in the PC versions of Grand Theft Auto games, you are generally required to add/replace DFF and TXD files in a file called gta3.img. This has been made possible thanks to numerous developers in the community producing tools, the most popular are linked to below.
- IMG Tool 2.0, by Spooky (for GTA3, GTAVC and GTASA)
- IMG 1.0, by REspawn, also contains French and German language files