https://www.thedigitalpictureframe.com/the-best-3-image-viewers-for-your-raspberry-pi-digital-picture-frame-project/

$ feh -qrYzFD120 –zoom fill /home/pi/Pictures/your-images

where:

q = quiet mode, 
r = recursive, 
Y = hide pointer, 
z = randomize, 
F = full screen, 
D120 = delay of 120 seconds and 
zoom fill = fills your screen.