Replace Sitecore.MediaRequestHandler in web configuration with a patch file inside the handlers.

Existing one:

`<add verb="*" path="sitecore_media.ashx" type="Sitecore.Resources.Media.MediaRequestHandler, Sitecore.Kernel" name="Sitecore.MediaRequestHandler" /`>

custom handler:

<add verb="*" path="sitecore_media.ashx" type="example.example.example.Processors.CustomMediaRequestHandler, example.example.Redirects" name="Sitecore.MediaRequestHandler"/>