Some of the filetype: search types, such as "bitmap" or "drawing", are very un-intuitive and hard to remember. We may want to consider creating a configuration where aliases for existing types are specified, so for example one can do filetype:photo and find photos by translating "photo" to "bitmap".
For more info - threads here: https://lists.wikimedia.org/pipermail/wikitech-l/2016-November/086995.html
and here: https://lists.wikimedia.org/pipermail/discovery/2016-November/001355.html