TEX is a file format for compressing textures image in Don't Starve. It is a derivative of DXT (S3 Texture Compression) file format. You may find some unimplemented items and character portraits by opening TEX files in Don't Starve game files.
Most images or icons in this wiki are directly converted from the TEX files in the game files.
TEX files of Don't Starve usually locates under
Here is the list of useful TEX location:
When you are doing actions involving core game files, you should be careful and make a backup.
To read TEX file, you are required to decompress TEX into any visible image format (usually PNG).
Here is the tool provided by Matt, TEXTool.
A modding guide with instructions on how to use the tool can also be found here.