I always forget these things and the man page is pretty large.

First off, the configs are ~/.config/feh/buttons for mouse, and ~/.config/feh/keys for keys. Some are the defaults, which I put there as a sort-of cheatsheet, so let’s start with my configs:

buttons:

pan             1
toggle_menu     3
zoom            2
zoom_in         4
zoom_out        5
rotate          C-3

keys:

toggle_actions          a
toggle_filenames        d
toggle_fullscreen       f
toggle_fixed_geometry   g
toggle_info             i
toggle_menu             m
reload_image            r
quit                    q
toggle_aliasing         A
toggle_auto_zoom        z Z
flip                    underscore
mirror                  bar
zoom_in                 plus Up
zoom_out                minus Down
zoom_fit                0 C-z
orient_3                less
orient_1                greater
prev_dir                bracketleft
next_dir                bracketright

more (defaults):

close                   x               # close just one window
jump_random             z               # I've clobbered this...
jump_first              Home
jump_last               End
jump_fwd                page up
jump_back               page down
remove                  Delete
delete                  Ctrl+Delete
zoom_fit                /               # I've changed this to C-z
zoom_fill               !

Moving on, useful command line flags:

-x, --borderless        borderless
-F, --fullscreen        start fullscreen
-g, --geometry          like any good X program
--keep-zoom-vp          keep zoom when scrolling
-p, --preload           preload
-r, --recursive         recurse
-., --scale-down        make images fit window
-|, --start-at          start from the middle of a large collection
-f, --filelist          load image paths from file
-l, --list              ls thing
-w, --multiwindow       open each image in its own window
-S, --sort              by name, filename, dirname, mtime
-t, --thumbnails

As always, see the man page: feh(1)