What Makes A Good Submission/The Textures Resource
The Texture
The Texture Format
Textures should be submitted in the PNG format. This is due to the fact that it is a lossless format, so it never decreases the quality of the image. As well, GIF is another lossy format that is not accepted, as it loses colors and only supports 256 colors. However, there is only one other time that you may have to submit another format, which is the JPG format. When you have a game that has JPG textures, leave them in the JPG format. As JPG is a lossy format, converting them to PNG unnecessarily increases the image's file size, so it's best to leave it as JPG.
Texture Transparencies
If a texture has transparencies, don't remove them. The textures are applied to the model and removing them can make applying them harder.