From Sonic Retro
This template automatically assigns screenshots that have a system-specific screenshot template to a category based on its file extension, such as Category:JPEG screenshots.
Sonic Retro prefers PNG format for screenshots, since they're lossless and usually smaller and better quality than JPEG and GIF. The extra categories are used to make it easier to identify which screenshots should be replaced.
For more information, see Sonic Retro:Screenshots.
This template is included by the system-specific screenshot templates, so there is usually no need to include it manually.