The Derivicon (DERIVative favICON) module adds a Context module reaction allowing for Image style powered favicon derivatives to be applied.
Derivicon was built to help with identifying different server environments at a glance of the browser tab.
Derivicon was written and is maintained by Stuart Clark (deciphered).
Important note As the GD library doesn't support .ico files, it is recommended that you either use PNG files (renamed as .ico) as favicons, or install ImageMagick.
Drupal core Image module