The mimeconf file

mimeconf specifies how the different MIME types are handled for indexing, and which icons are displayed in the recoll result lists.

Changing the parameters in the [index] section is probably not a good idea except if you are a Recoll developer.

The [icons] section allows you to change the icons which are displayed by recoll in the result lists (the values are the basenames of the png images inside the iconsdir directory (specified in recoll.conf).