As mentioned on the License page, The Fat Gamer uses content, both imagery, and game content (why re-invent the wheel if you don’t have to, right?).
Here is as list of all sources – please note that The Fat Gamer references sources on the posts generally under the content and as part of the Game Details widget.
The groovy game system logos are pulled from the Retrosystem XMB theme images from retroarch-assets on Github.
For category summaries, I refer to Wikipedia for relevant descriptions.