Feh

Feh is a command line based tool that helps image display.
This has sub-second image opening, extremely performant and light weight

Operation

Display images in a directory

feh <directory>

Display images in a directory and its sub directories

feh <directory> --recursive

Display images with zoom

feh <directory> --auto-zoom

Display images scaled to screen

feh <directory> --scale-down

ref: https://linux.die.net/man/1/feh